Class 




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cuboright DEBosm 



A REVISION OF 



Bastin's 

College Botany 

For the use of Students of 'Pharmacy, 



&y 
WILLIAM BAKEK DAY 

Professor of Botany and Materia Medica in the 
School of Pharmacy of the University of Illinois, 



FIRST EDITION 

with 620 Illustrations 



CHICAGO 

G. P. ENGELHARD &- CO. 
1920 



<&& 



Copyright 1920 
By G. P. Engfxhard & Co. 



NOV 22 1920 



©CU604442 



CONTENTS. 



Introduction. 



Page. 



Definition and Scope of Botany — Departments of Botany — 

Order of Treatment 13-14 



PART I.— ORGANOGRAPHY, 

General Considerations — Classification of Plant Organs — 

Organs of Vegetation 15-16 



Chapter I. 

THE ROOT. 

Definition — Uses of Roots — Structure and Mode of Branch- 
ing — How Roots Differ from Stems — Absorbing Sur- 
face Exposed by Roots — Modifications Roots Undergo 
— Mycorhizas Shapes of Roots — Classification of Roots 
— Practical Exercises 16-20 

Chapter II. 

THE STEM. 

Definition — How it Differs from the Root — Uses of the 
Stem — Buds, Their Nature and Kinds — Different 
Kinds and Modifications of Above- Ground Stems — 
Size of Stems — Shapes of Stems — Direction of Growth 
— Duration of Stems — Habits of Growth — Under- 
ground Stems — Rhizomes — Tubers — Corms — Bulbs — 
Leaf-like Stems — Classification of Stems — Practical 
Exercises 20-32 

Chapter III. 

THE LEAF. 

Definition and Description of Leaves — Prefoliation or 
Vernation — Phyllotaxy — Duration of Leaves — Posi- 
tion of Leaves — Parts and Structure of Leaves — 
Venation of Leaves — Shapes of Leaves — Simple 
Leaves — Compound Leaves — Leaf Surface — Texture 



4 CONTENTS. 

of Leaves — Specially Modified Leaves — Practical 
Exercises 32-55 

Chapter IV. 

THE BRANCHING OF ORGANS. 

Dichotomous Modes — Monopodial Modes — Practical 

Exercises 55-57 

Chapter V. 

THE FLOWER. 

Nature of the Flower — Reasons why the Flower possesses 
Special Scientific Interest — The Flower, a Modi- 
fied Branch 57-60 

Chapter VI. 

ANTHOTAXY. 

Definition — Types of Anthotaxy — Forms of Indeterminate 
Anthotaxy — Forms of Determinate Anthotaxy — 
Mixed Anthotaxies — Recapitulation — Practical Exer- 
cises 60-68 

Chapter VII. 

PREFLORATION OR ^ESTIVATION. 

Definition and Kinds of Prefloration — Forms of Valvate 
Prefloration — Forms of Imbricate Prefloration — Con- 
torted Prefloration — Plicate Prefloration — Recapitula- 
tion of Prefoliation and Prefloration. — Practical 
Exercises 69-71 

Chapter VIII. 

STRUCTURE OF THE FLOWER. 

Parts of the Flower — Typical Flower — Deviations from 
Typical Form — Deviations due to Suppression of Parts 
— Deviations due to Multiplication of Parts — Devia- 
tions due to Anteposition of Parts — Deviations due to 
Irregularity of Parts — Deviations due to Union of. 
Parts — Practical Exercises r ., ., 71-76 

Chapter IX. 

THE TORUS, CALYX AND COROLLA. 

The Torus, or Receptacle — The Calyx — Forms and Modi- 
fications of the Calyx — Epicalyx — The Corolla — The 



CONTENTS. w 5 

Complete Petal — Forms of Choripetalous Corollas — 
Forms of Gameopetalous Corollas — Practical Exer- 
cises 76-82 

Chapter X. 

THE STAMENS, OR ANDRCECIUM. 

Structure of the Stamen — Insertion of Stamens — Union 
of Stamens — The Filament — The Anther — The Con- 
nective^ — The Pollen — Pollinia — Practical Exercises. . 82-87 

Chapter XL 

THE PISTILS, OR GYN^CIUM. 

Structure and Parts of the Pistil — Apocarpous and Syn- 
carpous Pistils — Placentation — The Ovary — The Style 
—The Stigma — The Ovule — Practical Exercises. .... 88-94 

Chapter XII. 

POLLINATION AND FERTILIZATION. 

Pollination Denned — Cross-pollination the Rule — Agencies 
of Cross'-fertilization — Structure of Anemophilous 
Compared with that of Entomophilous Flowers- 
Means by which Self-fertilization is Prevented — 
Diclinism — Dichogamy — Greater Potency of Foreign 
Pollen — Heteromorphism — Special Contrivances — 
Process of Fertilization — Gametes and Gameto- 
phytes — Development of Embryo — Practical Exercises 94-111 

Chapter XIII. 

THE FRUIT AND THE SEED. 

The Fruit Denned — Changes in Process of Development 
— Agencies of Dispersion — Classification of Fruits — 
Description of Principal Kinds — Recapitulation of 
Fruits — 

Definition of the Seed — Changes during Development from 
the Ovule — Structure of the Seed — Parts of the Seed 
— The Embryo — Kinds of Embryos — Position and 
Folding of Embryo — The Number of Seeds produced 
by Plants — Practical Exercises 111-130 



6 CONTENTS. 

PART II.— HISTOLOGY. 
Chapter I. 

THE CELL. 

The Cell in General — The Protoplast Qualities inher- 
ent to the Protoplast — Growth of the Cell — Parts of 
the Protoplast — The Plastids — Chromatophores — 
Chloroplasts — Chromoplasts — Other Cell Contents — 
Starch — Inulin — Sugars — Other Carbohydrates — 
Fixed Oils and Fats — Proteins — Aleurone — Enzymes 
— Glucosides — Pentosides — Alkaloids — Tannins — Vola- 
tile Oils — Resins, Oleo-resins, Gum-resins and Bal- 
sams — Acids — Mineral Substances — Calcium Oxalate 
Crystals— The Cell Wall— Modifications of the Wall- 
Cellulose — Ligno-cellulose — Cutin or Suberin — Muci- 
lage — Mineral Substances — Stratifications — Growth 
of the Wall — Practical Exercises 131-168 

Chapter II. 

THE FORMATION OF CELLS. 

Reproduction of Cells — Indirect Nuclear Division or 
Karyokinesis — Reduction Division — Free Cell Forma- 
tion — Budding — Direct Nuclear Division — Practical 
Exercises 168-175 

Chapter III. 

THE TISSUES, THEIR ORIGIN AND CLASSIFICATION. 

Definition — Classification of Tissues — Meristematic Tis- 
sue — Primordial Meristems — Primary Meristems — 
Primary Permanent Tissues — Secondary Meristems 
— Secondary Permanent Tissues — Parenchymatous 
Tissues — Parenchyma — Collenchyma — Sclerotic Tis- 
sue — Epidermal Tissue — Stomata — Trichomes — Endo- 
dermal Tissue — Cork — Prosenchymatous Tissues — 
Bast Fibers — Wood Fibers — Tracheids — Vascular Tis- 
sue — Sieve Tissue — Secretory Tissues — Latex Vessels 
— Secretory Cells — Secretory Passages — Glandular 
Hairs— Practical Exercises 175-216 



CONTENTS. 7 

Chapter IV. 

THE HISTOLOGY OF THE ORGANS. 

The Root — Growth of Roots — Primary Structure — Sec- 
ondary Changes — Secondary Structure — The Stem — 
Primary Structure — Fern Stems — Monocotyledonous 
Stems — Dicotyledonous Stems — Secondary Changes — 
Rings of Growth — Bark — The Leaf — Types of 
Leaf Structure— The Flower— Pollen — The Fruit and 
the Seed — Practical Exercises 216-253 



PART III.— PHYSIOLOGY. 

Chapter I. 

Scope of Plant Physiology — Properties or Attributes of 
Protoplasm — Resemblances and Differences between 
Animals and Plants 254-258 

Chapter II. 
Constituents of Plants — Food of Plants — Absorption of 
Water and Soil Solutions — Ascent of Water — Trans- 
piration — Gases in the Plant 259-268 

Chapter III. 
Elaboration of Food — Photosynthesis — Synthesis of Pro- 
teins — Distribution and Storage of Food Materials — 
Digestion — Symbiosis — Respiration — Growth — Influ- 
ence of Temperature on the Life of the Plant — 
Influence of Light on the Life of the Plant 268-280 

Chapter IV. 
Movements of Plants — Locomotion — Movements not Loco- 
motive — Geotropism — Heliotropism — Hydrotropism — 
Circumnutation — Nyctitropic Movements — Irritability 
— Reproduction 280-293 

PART IV.— TAXONOMY. 

Chapter I. 

Value of Comparative Study — Classification and Naming 

of Plants— Principal Groups of Plants 294-300 



8 CONTENTS. 

Chapter II. 

THE THALLOPHYTA. 

Characteristics of the Thallophytes — The Myxomycetes, or 

Slime Molds . . 300-304 

Chapter III. 

THE THALLOPHYTA (CONTINUED). 

The Schizomycetes, or Bacteria — The Cyanophyceae, or 
Blue Green Algae — The Flagellata — The Dinoflagel- 
lata, or Peridinae 305-312 

Chapter IV. 

THE THALLOPHYTA THE ALG^. 

The Diatomese, or Diatoms — The Heterocontae — The 
Chlorophyceae, or Green Algae — The Siphonales — The 
Protococcales — The Volvocales — The Confervales, or 
Confervoid Algae — The Conjugates — The Charales, or 
Stoneworts . . 312-332 

Chapter V. 

THE THALLOPHYTA THE ALG^E (CONTINUED). 

The Phaeophyceas, or Brown Algae — The Phaeosporales — - 
The Fucales, or Rockweeds — The Rhodophyceae, or 
Red Algae 333-339 

Chapter VI. 

THE THALLOPHYTA — THE FUNGI. 

General Characters — The Phycomycetes, or Algal Fungi — 
The Zygomycetales — The Peronosporales — Saproleg- 
niales — The Chytrideacese — The Ascomycetes, or Sac 
Fungi — The Erysipheae — The Plectascales — The Pyre- 
nomycetes — The Discomycetes — The Tuberales — The 
Saccharomycetes — The Exoasci 339-353 

Chapter VII. 

THE THALLOPHYTA — THE FUNGI (CONTINUED). 

The Basidiomycetes — The Uredinales — The Ustilaginales 
— The Gasteromycetes — The Hymenomycetes — The 
Fungi Imperfecti 353-363 



CONTENTS. 9 

Chapter VIII. 

THE THALLOPHYTA — THE FUNGI (CONTINUED). 

The Lichenes, or Lichens — Nature of Lichens — The Homoi- 
omerous Lichens — The Crustaceous Lichens — The 
Foliaceous Lichens — The Fruticose Lichens — Classi- 
fication 363-368 

Chapter IX. 

THE BRYOPHYTA, OR MOSS-PLANTS. 

Classification — General Characters — The Hepaticae, or 
Liverworts — The Ricciales — The Anthocerotales — The 
Machantiales — The Jungermanniales — The Musci, or 
Mosses — The Sphagnales — The Andrseales — The 
Bryales 368-379 

Chapter X. 

THE PTERIDOPHYTA, OR VASCULAR CRYPTOGRAMS. 

Classification — Characteristics — The Filicinese, or Ferns — 
The Qhioglossaies, or Adder's Tongue Ferns — The 
Filicales, or Ferns Proper — The Hydropteridales, or 
Water Ferns — The Equisetineas, or Horsetails — The 
Lycopodineae, or Club Mosses — The Lycopodiales — 
The Selaginallales 379-395 

Chapter XL 

THE SPERMATOPHYTA, OR SEED PLANTS. 

Classification — Characteristics — The Gymnospermae, or 
Gymnosperms — The Cycadales, or Cycads — The Conif- 
erales, or Conifers ; — The Gnetales, or Joint Firs.... 396-408 

Chapter XII. 

THE SPERMATOPHYTA (CONTINUED). 

The Angiospermae, or Angiosperms — General Characters 408-411 
Chapter XIII. 

THE SPERMATOPHYTA — THE ANGIOSPERMAE (CONTINUED) - 

The Monocotyledons — General Characters — The Pandan- 
ales — The Heliobales — The Glumales — The Palmales — 
The Arales — The Farinales — The Liliales — The Sci- 
taminales— The Orchidales 408-416 



10 CONTENTS. 

Chapter XIV. 

THE SPERM ATOPHYTA — THE ANGIOSPERMiE (CONTINUED). 

The Dicotyledons — General Characters — The Archi- 
chlamydeae, or Apetalae — The Polypetalae, or Dialy- 
petalae — The Sympetalse, or Gamopetalae — Orders and 
Families of the Dicotyledons 417-432 

Chapter XV. 

EVOLUTION. 

General Considerations — Darwinism — The Struggle for 
Existence — The Survival of the Fittest — Objections 
and Difficulties — Continuous Variations — Mutations 432-438 

Chapter XVI. 

HEREDITY. 

Definition of Heredity — Significance — Mendelism — Men- 
del's Law of Dominance — Unit Characters — Purity of 
Gametes — Phenotypes and Genotypes 438-444 

Chapter XVII. 

ECOLOGY. 

Scope of Ecology — Problems — Ecological Factors — Light 
— Water — Soil — Wind — Other Plants — Animals — 
Plant Societies — Water Plants — Swamp Societies — 
Normal Plants — Desert Plants — Seacoast Plants — Suc- 
cession of Plant Societies — Important Eelation to 
Medicinal Plants 445-455 



PREFACE. 



Introductory courses in botany are well established in the cur- 
riculums of pharmaceutical colleges and schools. While the imme- 
diate purpose of these courses is preparation for the study of the 
vegetable drugs, yet their value as a part of the student's general 
education is not less important. The fundamental facts and prin- 
ciples of botany are the same, whatever application may be made 
of them; by linking these facts and principles to the student's 
major subject, pharmacy, a considerable gain in interest is secured. 

Bastin's College Botany has served a useful purpose as a text- 
book in many colleges of pharmacy. It is thirty years since the 
book was first published. At that time Professor Bastin taught 
botany and materia medica in the Chicago College of Pharmacy, 
which later became the School of Pharmacy of the University of 
Illinois. As a student under Professor Bastin and as his successor 
in the subjects taught by him in the School of Pharmacy, it has 
seemed fitting that the writer should undertake the revision of 
this useful text book. 

In this revision, Professor Bastin's plan of dividing the text 
into four departments has been adhered to. ^ An advantage in this 
plan, from the point of view of the teacher, is that it permits of 
the presentation of the subject from any one or more of several 
sides, to suit the time, facilities and material available. Thus 
some schools will begin with Organography, others with Histology, 
yet others with Taxonomy. Or two or more of these subjects may 
be presented concurrently. 

In the choice of illustrative material, an effort has been made 
to use medicinal plants so far as this was feasible. 

Part I, Organography, has required but few changes. In 
Part II, Histology, many new illustrations have been introduced, 
and the text has been recast. Part III, Physiology, has been 
largely rewritten, and Part IV, Taxonomy, has been rewritten and 
considerably extended. 

One hundred and thirty-five figures new to the book have been 
added, replacing ninety-four of the figures formerly used. Of the 
new illustrations, sixty are from original drawings by my col- 



12 PREFACE. 

league, Professor E. N. Gathercoal, to whom grateful acknowledg- 
ment is made. Forty figures are taken from other text books, and 
due credit has been given in each instance. 

It has not been deemed wise to add to the size of the book by 
including descriptions of processes and methods or by incorporat- 
ing lists of apparatus, stains, mounting media, etc.; for such, 
the reader is referred to the many excellent special works on these 
subjects. The practical exercises in Parts I and II have been 
retained, as offering useful suggestions for both teacher and 
student. 

August 25, 1920. William B. Day. 



INTRODUCTION. 



Botany may be defined as the science of plants. In its broadest 
; ;ense it includes all classified knowledge of vegetable organisms 
from the lowest to the highest. A science of such scope has, of 
course, many branches, each of which is the outgrowth of special- 
ized study. For example, plants may be considered with reference 
to the parts or organs of which they are composed and the changes 
and adaptations that different organs undergo, as well as the 
minute structure of these parts, giving rise to the department of 
morphology, and comprising' outer morphology or organography 
and inner morphology or histology. Included in the latter are 
embryology, which deals with the origin and development of the 
individual plant, and cytology, which treats of the structure and 
behavior of cells themselves. Plants may also be regarded with 
reference to the functions of the various organs — the way they 
perform their work of vegetation and reproduction — and this view 
gives rise to plant physiology ; likewise we may compare and 
classify plants according to their resemblance and differences, thus 
pursuing the study of plant classification, taxonomy or ^systematic 
botany; once more, we may observe them with reference to the 
adaptation of the plants themselves or of their parts to their sur- 
roundings or environment, this being known as ecology, or we may 
notice their distribution over the earth's surface or their occur- 
rence as fossils in earth's crust, thus entering upon the study 
of geographical botany and paleobotany, respectively; and, lastly, 
we may regard plants in the light of their economic uses or their 
relations to human welfare, thus leading to the various branches 
of plant industry or economic botany, including not only the older 
applied sciences of agriculture, horticulture, floriculture, forestry, 
pharmaceutical and medical botany, but the newer sciences of 
plant pathology and plant breeding as well. 

For the purposes of this work the subject is treated mainly 
under four heads, as follows: 



Part I. Organography or Outer Morphology, that branch 
of structural botany which treats of the organs or 
instruments with which plants do their work, as 
roots, stems, leaves, parts of flowers, etc., — their 
forms and modifications. 

Part II. Histology, that branch of structural botany which 
treats of the minute or microscopic structure of 
plants. 

Part III. Physiology, that branch of botanical science that 
treats of the functions of plants and their organs; 
that undertakes to explain how the plant and its 
various parts perform their work. 

Part IV. Taxonomy. Under this head is considered the mode 
of naming and classifying plants, and a brief 
account of the more important groups of plants is 
given. 

Some subjects which cannot be strictly included under any of 
the above heads are also briefly treated. 



PART I. 

ORGANOGRAPHY. 

GENERAL CONSIDERATIONS. 

The lowest forms of plant life are so simple in their structure 
that they can hardly be said to possess distinct organs or parts 
for the performance of different kinds of work. With them, so 
to speak, the work of vegetable life is performed without imple- 
ments, in the rudest manner. But as we pass up the scale of 
vegetable life we find plants growing more and more complex in 
their structures, the plant body tends more and more to be differ- 
entiated into organs, till at last, when we reach the highest group, 
the flowering plants, we find it to consist of a variety of parts, 
each differing from the other in appearance and structure, and 
each contributing in a somewhat different way to the life of the 
whole organism. Our study, therefore, of organography will be 
mainly confined to the organs of the higher plants, where we find 
them most highly developed. 

In flowering plants we observe two kinds of organs; first, the 
vegetative, or those which are concerned chiefly with the elabora- 
tion, transportation and storage of food and which therefore con- 
tribute to the vegetative life of the plant; and second, the repro- 
ductive, or those whose special function it is to reproduce the 
species. 

The vegetative organs consist of roots, stems, and leaves. All 
of these organs occur under numerous modifications. The same 
plant may bear several different kinds of each of them, some 
adapted to one use, others, perhaps, to quite a different one, so 
that what is, morphologically speaking, the same organ, may per- 
form a variety of quite distinct functions. It is not Nature's 
method to create new organs when new uses are required, but to 
reshape and modify already existing ones, and fit them for the 
new requirements. If, for example, it is of advantage to the plant 



16 PART I. — ORGANOGRAPHY. 

to climb, a leaf or a branch is converted into a tendril, or if the 
good of the species requires that it be defended against predacious 
animals, branches or leaves are modified into thorns. 



THE ORGANS OF VEGETATION. 

The flowerless plants below the mosses show, in rare instances, 
an indistinct differentiation of stem and leaf. In the mosses the 
distinction becomes sharp and clear, but they do not possess roots. 
It is not till we reach the Pteridophytes, or highest group of flower- 
less plants, that we find a complete differentiation of all the vege- 
tative organs. The order of their evolution, therefore, seems to 
be: First, the shoot composed of leaf and stem, and last, the root. 
In complexity of structure, roots rank lowest and leaves highest. 
It must be borne in mind, then, that in discussing these organs 
of the plant, we are describing types only and that the organs 
themselves are not immutable, but that various gradations may 
exist between them. 



CHAPTER I.— THE ROOT. 

The root may be defined as the descending axis of the plant; 
it is that part of the plant-axis which does not bear leaves. Roots 
are ordinarily subterranean in their habits, and serve the double 
use of attaching the plant securely to the soil and of enabling it 
to absorb from it the necessary water and minerals. These are 
their normal uses, but they sometimes take upon themselves addi- 
tional functions. The roots of the Carrot, Beet and Turnip, for 
example, not only subserve these functions, but also that of store- 
houses for food. These plants are biennials, and during the first 
year of their growth they store away in their fleshy roots great 
quantities of nutrient materials, which, during the succeeding 
year are expended in the production of flowers and fruits. Many 
perennial herbs, like the Dahlia, though the above-ground parts 
perish at the close of every season, are able to survive by means of 
their under-ground parts, because they store away, year by year, 
in their tuberous roots, the materials necessary for the succeeding 
year's growth. The famous Banyan tree of India sends downward, 
from its huge horizontally spreading branches, roots which make 
their way to the soil, and serve not only the ordinary uses but also 



CHAPTER I. — THE ROOT. 



17 



that of props or subsidiary stems to support the weight of the 
branches. 

But there are many instances of roots whose habits and func- 
tions are quite different from the ordinary. The roots of air 
plants or epiphytes, like those of many tropical orchids, for exam- 
ple, never reach the soil at all, but cling to the bark of trees and 
absorb moisture from the air ; the rootlets that spring out laterally 
from the stems of the Poison Rhus, Trumpet Creeper and Ivy, 
Fig. 1, serve purely the use of climbing organs; those of the 
Mistletoe and Dodder penetrate the bark of the plants on which 
they find lodgment, and live at the expense of the nutritious juices 

absorbed from their hosts. 
Similar parasitic roots, but 
underground, are formed by 
many plants, notably the 
giant Rafflesia of tropical 
forests. 

Roots differ from stems in 
some important particulars, 
notably the following: They 
are much less regular in 
their mode of branching, 
they are simpler in their in- 
ternal structure, -they do not 
directly bear leaves or leaf- 
rudiments, their growing- 
point is located just back of 
the apex instead of at the 
apex, and in consequence of 
this sub-apical growth, the 
tip, unlike that of the stem, 
becomes covered with a pro- 
tecting sheach or cap of older 
and thicker-walled cells, technically called the root-cap, which 
affords it a decided mechanical advantage in penetrating the soil. 
The absorbing surface exposed by roots to the soil is much 
greater than is usually supposed. In most plants it is probably 
comparable in extent with that exposed* by the leaves to the air. 
This great superficial area which roots present to the soil is due 
partly to their repeated ramifications into fine divisions, and partly 
to the numerous delicate root-hairs that are found on the ultimate 




Fig. 1. — Portion of stem of Ivy show- 
ing rootlets. 



18 



PART I. — ORGANOGRAPHY. 



branches just back of the growing point. The finer root-branches, 
together with their attached hairs, are the chief agents by which 
the plant absorbs water and solutions of minerals from the soil, 
and on them, therefore, more than on the larger roots, is the life 
of the plant dependent. The principal reason why transplanting 
in midsummer is so dangerous to the life of the plant, is that in 




Fig. 2. 




Fig. 2. — A root-tip considerably magnified, 
hair ; c, the root-cap. 

Fig. 3. — The tap-root of the common Stock. 

Fig. 4. — The clustered and tuberous roots of the Dahlia 



Fig. 4. 

the growing point ; b, root- 



the process of digging up and re-setting, numerous root-tips with 
their absorbing hairs are broken off and destroyed, so that the 
leaves evaporate water much faster than it can be taken up by 
the remaining roots, and the plant, therefore, necessarily withers. 
As soon as new hairs are formed, the absorption of water is 
resumed and the plant recovers from its wilted condition. Fig. 2 
represents a root-tip considerably magnified, showing its growing- 
point a, its root-hairs b, and its root-cap c. 

A curious modification of the root is the presence of a fungus, 
either inside or outside of the root, which replaces the root hairs 
and carries on their absorbing function. Many forest trees, as 
well as Heaths and Orchids, have this partnership with a fungus, 
termed a mycorhiza. It will be more fully considered in a later 
chapter. 

Eoots may be classified into primary and adventitious. A 
primary root is the downward continuation of the embryonic root 
of the seed. Commonly it is simple, or the branches it produces 
are small as compared with the main root; in this case it is called 



CHAPTER I. — THE ROOT. 



19 



a tap-root. Fig. 3 represents the tap-root of the common Stock. 
Sometimes, however, the embryonic root almost immediately breaks 
up into numerous similar branches, forming multiple primary 
roots. These may become thickened and tuberous, as in the Dahlia, 
Fig. 4, or they may remain slender and fibrous, as in the roots of 
the Plantain. 

Not infrequently the primary root disappears altogether at an 
early stage of the development of the plant, and is replaced, func- 
tionally by other roots springing out laterally from the stem higher 
up. This is almost universally the case with the large group of 
flowering-plants called Monocotyledons, typified by the Lilies, 
Palms, Grasses and Sedges, and with the higher flowerless plants, 
such as Ferns, Club-mosses and Horse-tails. Roots of this charac- 
ter and all others which originate laterally from stems, branches 
or leaves, whether above ground or beneath it, are called adven- 
titious roots. Such are the aerial roots of the Ivy, illustrated in 
Fig. 1, the roots which spring from the branches and above-ground 



1 



Fig. 5. 





Fig. 6. 



Fig. 8. 



Fig. 5. — Fusiform root of the Radish. Fig. 7. — Nodose roots of the Dropwort. 
Fig. 6. — Napiform root of the Turnip. Fig. 8. — Fibrous roots of a Grass. 



stems of various species of the Fig, from the joints of some grasses, 
and from the rhizomes or underground stems of such plants as 
Podophyllum, Serpentaria and Iris. 

It is often convenient to describe roots by their shapes. That 
of the Carrot, which is thick at the base and tapers gradually to 
the apex, is called conical; one which is shaped like the root of 
the Radish, Fig. 5, is called fusiform; one shaped like that of the 
Turnip, Fig. 6, napiform; roots like those of the Dropwort, Fig. 7, 



20 



PART I. — ORGANOGRAPHY. 



nodose; roots like those of the Sweet-potato and Dahlia, Fig. 4, 
tuberous; and roots which are wholly slender and thread-like, as 
those of most grasses, Fig. 8, fibrous. 



Origin 



Classification of Roots. 



( Adventiti 
( Primary— 



ous — from other parts of the stem, 
from the embryo 



Function 



Roots. 



Fix the plant in the soil. 
Normal J Imbibe soil solutions. 

Serve as storehouses for water and 
food. 

/ Act as holdfasts for epiphytic plants. 

Anomalous < Imbibe juices from host plants 
( for parasites. 



Consistence 



{Fleshy ( Conical 

1 Napifor 
< Fusifor 
j Tubero 
Fibrous I Nodose 



orm 
iform 
Tuberous 
se 



Practical Exercises. 

Cause some seeds of common plants, as the Pumpkin, Pea, Corn, etc., to 
germinate over water so that the roots do not pass into the soil. A convenient 
way is to fill a wide-mouthed bottle half or two-thirds full of water, and, after 
fitting a cork to it, fasten by means of wires the seeds to the under surface of 
the cork, and insert it in the mouth of the bottle, and set the latter away for a 
few days in a warm place. The seeds will soon germinate, and the forms of 
their roots, and their structure and habits of growth, may be studied. 

Observe and describe the forms and modes of branching of the different 
roots ; by means of the magnifying lens study the root-hairs, observing on what 
parts of the rootlets they are most abundant ; determine whether the roots are 
primary or secondary in their character, and examine the tips of the roots for 
the root-cap. Procure specimens of the common Duck-weed, in which the 
root-cap is highly developed, and examine it with care. As examples of aerial 
roots, study those of the Ivy, and as examples of the roots of parasites, study 
those of the common Doader or of the Mistletoe, making sections of them and 
of their host-planes in sucn a way as to observe how the roots penetrate the 
bark of the host. 

Record, in appropriate descriptive language, and by means of drawings, the 
results of your observations. 



CHAPTER II.— THE STEM. 

The stem may be described as that part of the plant which 
bears all of the other organs. The stem, therefore, is indispensable, 
there being none of the higher plants that are truly stemless. It 
is commonly the ascending axis of the plant, while the root is the 
descending axis. The ordinary functions of the stem are to form 



CHAPTER II. — THE STEM. 21 

such a support for the leaves as will expose them to the light and 
air, to bear the floral organs and convey to them the nutriment 
they require, and to form a means of communication and inter- 
change between the roots, the organs which absorb the watery 
solutions from the soil, and the leaves, the organs which utilize 
these materials in the elaboration of the plant food. But, like 
other vegetative organs, stems are often modified, as we shall 
presently see, so as to subserve functions quite different from the 
normal. Besides bearing roots and leaves — appendages different 
from itself — a stem, commonly, though not always, bears branches, 
or appendages essentially like itself. A stem differs from a root 
not only in the fact that it is leaf-bearing, but in having its 
branches, for the most part, arranged with mathematical regular- 
ity, and that the growing-point is strictly apical instead of sub- 
apical. A stem usually increases in length by the growth of a 
terminal bud, and its branches commonly originate from buds 
which spring from the angle where the leaf joins the stem. We 
should first understand the nature of buds. 

Buds are in reality rudimentary stems, with rudimentary leaves 
compactly arranged upon them. In the growing season we observe 
them constantly unfolding. The short bud-axis which bears the 
minute, closely packed leaf-rudiments is constantly lengthening 
below, carrying the rapidly expanding leaves farther apart and 
developing into a leafy branch, while above, the bud is continually 
being renewed. Such a bud is not covered with scales. Its leaves 
are all destined to develop into foliage. 

On some trees the buds that exist during the season of rest 
are similar, except as respects the stoppage of their growth, to 
those of the growing season. Such buds are usually of very small 
size, and in some cases they are wholly or partially concealed 
beneath the corky layer of the bark. Buds of this kind are called 
naked buds. 

But most of our northern trees, at the approach of the cold 
season, form scaly buds, which differ from those of the growing 
season by having the outer leaf-rudiments transformed into scales 
which never develop into true leaves, but whose sole function is 
to protect those within, which in the spring are destined to 
develop either into foliage or into floral organs. Such buds are 
usually conspicuous, and they often attain a considerable size, as, 
for example, in the Hickory. 

The scales of scaly buds are admirably adapted for protective 



22 



PART I. — ORGANOGRAPHY. 



purposes. They contain but little water, and are therefore bad 
conductors of heat, thus preventing the occurrence of too sudden 
changes of temperature in the interior of the bud. In many in- 
stances they have either a lining of downy hairs or are covered 
with an insoluble varnish. They serve to prevent the drying out 
of the soft and delicate parts within and also in a measure to 
protect these from being injured by birds or insects. 

Fig. 9 represents a twig of the Ohio Buckeye as it appears in 
the late autumn or early spring. At the apex is a large scaly bud; 
below, situated in the axils of leaf scars, are smaller axillary 

buds. Fig. 10 is a longitud- 
inal section of one of the 
large terminal bud? of the 
same tree, showing the very 
short axis and compactly 
arranged leaf-rudiments. 

Buds normally occur as 
represented in Fig. 9, either 
at the ends of the stems, 
when they are called term- 
inal buds, or in the axils of 
leaves, when they are called 
axillary buds; sometimes, 
however, they occur in other 
situations on the stem, and 
occasionally they are formed 
on roots or even on leaves; in 
all these casas they are term- 
ed adventitious buds. 

Examples of buds of this 
kind occur occasionally on 
the American Elm when the 
surface of the stem has been 
abraded or irritated,, causing an extra supply of nourishment to 
flow to the spot; the compact bunches of twigs sometimes seen on 
these trees originate from such buds; the shoots which often arise 
in great numbers from the trunk of a pollarded willow have a 
similar origin; the leaves of Bryophyllum, when they have been 
shed, habitually produce marginal buds that, under favorable con- 
ditions, root and form new plants (see Fig. 11), and the occurrence 
of adventitious buds on the roots of some species of Poplar, causes 




Fig. 9. Fig. 10. 

Fig. 9. — Portion of 
twig of Ohio Buckeye, 
natural size, with ter- 
minal and axillary 
buds, and leaf-scars. 

Fig. 10. — Enlarged 
view of longitudinal 
section of a terminal 
bud of the same tree, 
showing the manner in 
which the scales over- 
lap. 



CHAPTER II. — THE STEM. 23 

them habitually to send up shoots at a distance from the main 
trunk. 

It often happens, also, that more than one bud is formed in 
or near the axil of the leaf; extra buds of this kind are called 
accessory or supernumerary buds. Sometimes they are placed 
side by side, as on the Apple-tree, and this is more commonly the 
case, but sometimes they occur one above the other, as on the 
Butternut and Walnut. 

Because of lack of light or of insufficient supply of nourish- 
ment, buds frequently fail to develop, remaining quiescent until a 
favorable opportunity for growth is offered, such as that afforded 




Fig. 11.: — Leaf of Bryophyllum, with marginal buds. 

by the damage or destruction of the better located buds by late 
frosts, when these quiescent or latent buds develop into leaves or 
branches. If no such opportunity offers, latent buds finally disap- 
pear, being covered by the bark. 

Branches produced from large, strong terminal buds usually 
grow rapidly during the early summer and then form terminal 
buds, which thus prevent further growth in length during the 
remainder of the season. This mode of development is termed 
definite annual growth. Other stems may continue to lengthen by 
apical growth during the entire summer, with the result that their 
soft green tips are killed by the frost and the next year's growth 
is from axillary buds lower on the stem, where the tissues had 
matured sufficiently to successfully resist the cold. This is termed 
indefinite annual growth. 

If the development of a stem is entirely from one terminal bud 
there can be, of course, no branches, and we describe it as a simple 
stem or, better, as a columnar stem. An instance is the stem of 
the Palms. If branches are formed freely, but the main stem or 
trunk dominates the branches, as in the Pines, the stem is de- 



24 



PART I. — ORGANOGRAPHY. 



scribed as excurrent or spire shaped. If, however, the main trunk 
branches freely so as to be soon lost in the branches, we have the 
deliquescent type of stem, of which the common Elm tree is an 
excellent example. 

Size of Stems. Stems differ widely in this respect. Some, 
as those of certain mosses, are scarcely the one twenty-fifth of 
an inch in length, and the diameter does not exceed that of a fine 
thread, while those of the giant Sequoia of California, and a 




Fig. 12. 



Fig. 12a. 



Fig. 13. Fig. 13a. Fig. 14. 



Fig. IS. 



Fig. 12. — Terete or cylindrical stem of Basswood. 

Fig. 12a. — Flattened stem of Opuntia Cactus. 

Fig. 13. — Triquetrous or triangular stem of a species of Scirpus or Rush. 

Fig. 13a. — Quadrangular stem of Mint. 

Fig. 14. — Jointed stem of Barley. 

Fig. 15. — Fluted stem of Parsnip. 



species of Eucalyptus in Australia attain the remarkable height of 
more than four hundred and twenty feet. 

Shapes of Stems. In this respect stems differ no less widely. 
The ordinary or typical form is that of a cylinder, or rather a 
very much elongated cone; such a stem is described as cylindrical 
or terete (see Fig. 12) ; but sometimes it is flattened as in the 
stems of some species of Cactus, Fig. 12a; sometimes triangular, 
as in some species of the Rush, Fig. 13; sometimes square or 
quadrangular, as in many Mints and Scrophularias, Fig. 13a ; some- 
times jointed, as in the stems of the Grasses, Fig. 14; and some- 
times fluted, as in the stem of Valerian and that of the Parsnip, 
Fig. 15. In the so-called stemless or acaulescent plants, like the 
Dandelion, the stem is short and broad, forming a disk-like crown, 
from which the roots shoot downward and the leaves upward; and 
in the Cactuses, succulent Euphorbias and some other families of 



CHAPTER II. — THE STEM. 25 

plants, it assumes a great variety of irregular or oddly grotesque 
forms. 

Direction of Growth. In this respect also there is great 
diversity. The larger proportion of aerial or above-ground stems 
are upright or erect, but some are ascending, that is, they rise 
obliquely upward; some are reclining, or at first erect, but after- 
wards bending over as if too weak to stand; some are decumbent, 
or creeping along the ground, but with the apex ascending; some 
are procumbent or prostrate, that is, lying wholly upon the ground, 
and still others are repent, or creeping along the ground, rooting 
as they grow. 

Duration of Stems. There are wide differences in this 
respect also. Some attain their full size in a few days, and in a 
few days more completely disappear, while there are others that 
possibly endure for a thousand years, and the vegetable world 
presents almost every gradation between these two extremes. 

A stem which dies down to the ground at the close of the 
season is called herbaceous; an herb whose life terminates with 
the season, or which springs from the seed, blossoms, ripens its 
fruits, and dies completely all in the same season, is called an 
annual; if, however, the stem dies, but the underground parts 
retain their vitality, and growth is continued another season, 
during which the seeds are perfected, and it then dies completely, 
it is called a biennial; and if by underground parts the life of the 
plant is continued indefinitely, through a period of years, it is 
called a perennial herb. An aerial stem that is woody, freely 
branching from near the ground, and of small size, not more than 
two or three times the height of a man, is called shrubby or 
fruticose; if the stem is of small size and woody only at the base, 
it is described as an under-shrub or as suffruticose ; if the stem is 
woody with a single trunk, and rises not higher than twenty-five 
or thirty feet, it is called arborescent; and if similar to the last, 
but of larger size, rising to the height of thirty feet or more, it is 
termed arboreous. 

Kinds of Above-Ground Stems as Regards Habits of Growth. 
Among the more important of these are the following: 

The twining or voluble stem is one which tw-ists or coils about 
a support, as the stem of the Morning-glory, Fig. 16, and that of 
the Hop. 

The scandent or climbing stem is one that rises by attaching 



26 



PART I. — ORGANOGRAPHY. 



itself, by means of special organs modified for the purpose, to some 
extraneous support. There are various modes of climbing. The 
Nasturtium and Solarium jasminoides, for example, climb by means 
of sensitive petioles, Fig. 18 ; the true Ivy, and Poison Ivy by means 
of rootlets; the Grape and Boston Ivy by means of tendrils, Fig. 
17, and some species of the Kose and Bramble climb in a rude 




Fig. 16. — Voluble or twining Fig. 17. — Portion of the Fig. 18. — Portion 

stem of the Morning-glory. stem of Boston Ivy, showing of stem of Solanum 

branching tendril, provided jasminoides, a leaf- 

with terminal sucker-like discs, climber. 

way by means of hooked prickles. Tendrils also may be either 
modified branches, as in the Grape; modified leaflets, as in the 
Pea, or modified stipules, as in the Sarsaparilla. 

The Culm is the peculiar jointed stem of the Grasses and 
Sedges. It may be herbaceous, as in Wheat and Rye, or woody, as 
in the Cane and Bamboo. 

The Scape is a flowering stem destitute of true foliage leaves, 
as those of the Dodecatheon and Dandelion. 

The Stolon is a prostrate or declined branch, the end of which, 
on coming in contact with the soil, takes root, and ultimately gives 
rise to a new plant. The Currant and Black Raspberry afford 
examples. 



CHAPTER II. — THE STEM. 



27 



The Sucker is an aerial shoot that springs from an under- 
ground branch. This form of stem is illustrated in the Red Rasp- 
berry and Blackberry. 

The Runner is such a creeping and rooting stem as that of 
the Strawberry, Fig. 19. 

The Offset resembles a runner, but is shorter and usually gives 
rise to but one plant. It is illustrated in the common Houseleek. 




Fig. 19. — Strawberry plant producing a runner. 



Fig. 20. — Branching thorn 
of the Honey-locust. 



The Thorn or Spine is a stem modification which is hard, 
pointed and destitute of leaves, or nearly so; for example, the 
thorns of the Honey Locust, Fig. 20. Not all spines, however, are 
modified stems; some are modified leaves or portions of leaves. 
Prickles are hardened plant hairs and are therefore merely out- 
growths of the epidermis. 

Underground Stems. 

The stems so far described are all aerial or above ground, but 
there are also underground ones, which mimic the habits of roots. 
They may readily be distinguished from the latter by the fact 
that they bear scales or scale scars, in the axils of which buds not 
infrequently occur, and also by the fact that the growing-point is 
situated at the apex instead of just back of it. Its growing end is 
enveloped in scales, the representatives of leaves; it, therefore, 
like the above-ground stem, possesses a terminal bud. Various 
kinds of underground stems are distinguished, the more important 
of which are the following: 

The Rhizome is a creeping, underground stem, which grows 
Jiorizontally or obliquely, is more or less scaly or marked with 
the scars of scales, sends off roots usually more abundantly from 
the under surface, and commonly has its upper surface more or 



28 



PART I.— ORGANOGRAPHY. 



less distinctly marked with the scars or withered remains of the 
bases of aerial stems of previous years. The terminal bud is 
usually conspicuous. A rhizome may either be slender and exten- 
sively creeping, as in Couch-grass and Carex, Fig. 21, or thickened 
and fleshy, as that of Solomon's Seal, Fig. 22. 




Fig. 21. — Creeping rhizome of 
a species of Carex. 



Fig. 22. — Thickened rhizome of Solo- 
mon's Seal. 



The Tuber is a short and excessively thickened underground 
stem, borne usually at the end of a slender, creeping branch. The 
tubers of the Artichoke and Potato, Fig. 23, are examples. The 




Fig. 23.— Tubers of the Potato. (After Bailey.) 

creeping branches usually perish in autumn, setting the tubers 
free from the parent plant. Since they grow in the spring and 
produce new plants, they are efficient means of propagating the 



CHAPTER II. — THE STEM 



29 



species. They may readily be distinguished from tuberous roots 
like those of the Sweet-potato, by their "eyes," which are axillary 
buds. 

The Corm is an excessively thickened, erect, underground 
stem, covered with thin leaf-scales on the surface. The corms 
of Crocus and Colchicum are examples. Fig. 24 is a longitudinal 
section of a Crocus corm. At the base is a partially decayed corm 
of the previous year, and at the apex a large bud. 

The Bulb is composed of an excessively short, erect stem, 
covered with fleshy scales or leaf-bases, which constitute its prin- 





Fig. 24. 

Fig. 24. — Longitudinal section of the corm of the Crocus. 

Fig. 25. — Longitudinal section of the Onion, showing the structure of a 
tunicated bulb. 

cipal bulk. It is practically a form of bud. A bulb whose leaf- 
bases form concentric coatings, is called a tunicated bulb, and one 
whole scales are imbricated, the outer ones not enclosing the inner, 
is called a scaly bulb. The Onion, Fig. 25, is an example of the 
former, and the Lily, Fig. 26, of the latter. 

The frequent occurrence of underground stems is evidence of 
their value to the plants that possess them. Both food and water 
are stored in these succulent organs and strong buds are developed 
by them so that the plants so fortunately equipped are not only 
able to survive the resting season without material injury from 



30 



PART 



-ORGANOGRAPHY. 



cold or drouth but in the growing season that follows, they secure 
the advantages of an early start over their seedling competitors. 
Pi-actically all the early-flowering herbs are of this kind. 

It is an interesting fact, that many of these underground stems, 





Fig. 28. 

Fig. 26.— The scaly 
bulb of the Lily. 

Fig. 27. — Portion of 
flattened stem and leaf- 
like branches of Muhlen- 
beckia. 

Fig. 28. — The common 
Duckweed, the upper 
disk-like portion bearing 
marginal flowers, and 
sending down a root with 
a prominent root-cap, 
Fig. 26. Fig. 27. from the under surface. 

rich in stored food, are also supplied with poisonous principles 
which apparently serve to protect them against destruction by 
foraging animals or insects. 

Thus it happens that many rhizomes and fleshy roots are 
employed as drugs, and a few poisonous ones, such as Water-Hem- 
lock and Aconite, having the appearance of edible roots when fresh, 
are occasionally eaten by mistake, sometimes with fatal results. 

Leaf-Like Stems. 
Stems occasionally mimic leaves, both in form and function. 
This is the case with the leaf-like bodies on the stem of the 
green-house Smilax (Myrsiphylly<m) . Such stems are called 
cladophylla, and that they are really stems or branches and not 
leaves is evidenced by the fact that they occur in the axils of 
scales; are the product, that is, of axillary buds. Fig. 27 repre- 
sents a flattened branch of Muhlenbeckia, which performs at 
once the functions of leaf and stem, though true leaves are borne 
upon it. The stems of Cactuses also frequently assume leaf-like 
forms and perform the functions of leaves, the leaves themselves 



CHAPTER II. — THE STEM. 



31 



being present in the form of spines. Other instances of stems 
disguised as leaves are afforded by the common Asparagus and 
the European Ruscus. In Duckweed the functions of leaf and 
stem appear never to have been differentiated. An organ so con- 
stituted, and which is, properly speaking, neither leaf nor stem, is 
termed a thallus, Fig. 28. It is a rare thing among flowering plants 
to find leaf and stem thus blended or undifferentiated, but it is 
very common among flowerless plants. 

Classification of Stems. 



Functions. 



Bear and support leaves. 

Bear roots. 

Provide passageways for water and nourishment between roots 

and leaves. 

Bear reproductive organs. 

Serve as storehouses for water and food (fleshy stems). 

Assist in photo-synthesis (green stems). 

Afford a means of propagating the plant (offsets, runners, etc.). 



Manner 

of 
Growth. 



By Means of Buds. - 



Scaly or naked. 

Terminal, axillary or adventitious. 

Sometimes accessory or supernumerary. 

Occasionally becoming latent. 

Giving rise to branches, leaves and flowers. 

Definite and indefinite annual growth. 

Columnar, excurrent and deliquescent 

growth. 



Direction 

of 
Growth. 



Erect. 

Ascending. 

Reclining. 

Decumbent. 

Procumbent. 

Repent. 



Duration. 



Annual. 

Biennial. 

Perennial. 



Consistence, 
and 
Size. 



Habits 

of 
Growth. 



( Herbaceous or soft. 
\ Suffruticose or partly woody. 
J Fruticose or shrubby. 
\ Arborescent or tree-like. 
[ Arboreous, a tree proper, 

r Twining or voluble. 

Climbing or scandent. 
; Stolon. 

Sucker. 

Offset. 

Runner. 



Peculiar 
Forms. 



[ Culm. 
< Scape. 
I Cladophylh 



Underground 
Stems. 



Rhizome. 
Tuber. 
Corm. 
Bulb. 



Tunicated. 

Scaly. 



32 PART I. — ORGANOGRAPHY. 



Practical Exercises. 

1. Gather twigs of six or more different trees, such as occur in your neigh- 
borhood, for instance, the Sugar Maple, the American Elm, the Bass-wood, the 
Locust, the Cotton-wood and the Horsechestnut. It will be better for the pur- 
pose of this exercise if they be gathered in the late autumn or early spring. 
Observe the leaf-scars and their arrangement on each twig. Observe the termi- 
nal and lateral buds of each, and note in each instance which are the stronger 
or better developed ; note the positions of the lateral buds relative to the leaf- 
scars in each case ; note which of the trees bear scaly .and which naked buds ; 
selecting the twigs that have the largest buds, dissect carefully the terminal 
buds of each, observing, by means of the magnifying glass, the position, 
structure and arrangement of the bud-scales and of the true leaves which they 
enclose ; note how the scales -are adapted in each case to the purpose of protec- 
tion, and, lastly, observe the area on the twig ringed by the scars of the bud- 
scales of the previous year, and answer, if you can, the question why this part of 
the twig did not elongate the same as that portion of it which bore the true leaves. 

2. Cut off most of the blade of a leaf of the common Begonia, leaving only 
the basal portion and the petiole, and plant it in damp sand, keeping it moist 
and at a temperature of about 90° F., for a few days. If the experiment has 
been properly conducted, adventitious buds will make their appearance in the 
axils of the veins. 

Study the supernumerary buds on twigs of the Apple, Lilac and Butternut 
or Hickory, and note the difference of arrangement. 

3. Compare the shapes of the stems of the Bulrush, the Wheat, Pepper- 
mint, Yellow Dock, Wild Parsnip, Prickly-pear, Cactus and other familiar plants. 
Observe the twining stems of the Hop and Morning-glory, and note how they 
differ in their modes of twining. Observe how the Blackberry, the Wild Clem- 
atis, the Poison Ivy, the Virginia Creeper, the Pumpkin, the Pea and the Green- 
briar differ in their climbing organs and in their modes of climbing. 

Observe the defensive organs of the Gooseberry. Are they all of the same 
kind or not? Are they modified branches or not? Examine branches of the 
Barberry and Hawthorn, and determine the nature of their thorns, whether they 
are modified leaves or modified branches. 

4. Pull up the following plants by the roots, and examine the underground 
parts, determining whether they are roots, rhizomes, corms, tubers or bulbs, and 
give the reasons for your conclusion : Wild or Indian Turnip, Common Blue 
Violet, Dandelion, Wild Hyacinth, Blood-root and Sweet-flag. Make a careful 
dissection of an Onion bulb and a Crocus corm, and ascertain how they differ ; 
also make a careful comparative study of the Sweet-potato and the Irish potato. 



CHAPTER III.— THE LEAF. 

Leaves may be defined as stem-appendages which have their 
origin just back of the apex of the stem, are regularly arranged 
upon it, and consist of expansions of its tissues. 

Foliage leaves, which may be taken as the type, are, in the 
majority of cases, flattened, bi-laterally symmetrical, expanded 
organs, green in color and presenting a distinct upper and under 
surface. They differ usually from stems by maturing or complet- 
ing their growth first at the apex, and afterwards at the base, but 
in Ferns and in some compound-leaved Dicotyledons the basal por- 
tion matures first while the apex continues to grow. The primary 
functions of foliage leaves are the elaborating the plant food and 
the evaporation of water. These functions will be discussed in 
Part III (Physiology). Morphologically, leaves exist in numerous 
forms other than that of foliage, and in many instances perform 
functions altogether different. Several different modifications of 



CHAPTER III. — THE LEAF. 



33 



leaves may often be observed on the same plant. Indeed, there is 
no organ of the plant body which subserves so many different uses 
or exists under such a variety of disguises. But, however different 
their forms and functions may be at maturity, they are alike in 
the earliest stages of their growth, that is, in the very young bud. 
All alike begin as minute papillae or protuberances just back of the 
growing apex of the stem. Moreover, they always appear in acro- 
petal order, that is, the older ones are lower down, and, as the stem 
elongates, younger ones are found higher up on the stem. 

Prefoliation or Vernation. By this is meant the arrangement 
of the leaves in the bud, a matter of considerable importance to 
observe in the study of plants. We may study it from two points 






Fi S- 29. Fig. 30. Fig. 31. 

Fig. 29.— Young leaf of the Tulip-tree, illustrating reclinate or inflexed verna- 
tion. 

Fig. 30. — Young leaf of Oak, illustrating conduplicate vernation. 

Fig. 31. — Transverse section of a young leaf of the Wild Cherry, illustrating 
convolute vernation. 

of view; we may consider the individual leaf, how it is folded, bent 
or rolled, or we may consider how the leaves are arranged with 
reference to each other. 

Studying the individual leaf, we distinguish the following 
forms: If the apex is bent inward toward the base, as the leaf 
of the Tulip-tree, Fig. 29, it is described as reclinate or inflexed; 
if it is doubled inward on the midrib, so that the two sides are 
applied to each other, face to face, as in the Oak, Fig. 30, it is 
called conduplicate; when rolled inward from one margin to the 
other, as in the Wild Cherry, Fig. 31, it is said to be convolute; 
when rolled inward from the apex toward the base, as in the 
Sundew and in Ferns, Fig. 32, it is called circinate; when, as in 
the Birch, Fig. 33, it is folded somewhat like the folds of a fan, 
it is described as plicate; when, as in the common Violet, Fig. 34, 



34 



PART I. — ORGANOGRAPHY. 



it is rolled inward from each margin, it is termed involute; and 
when, as in Yellow Dock, Fig. 35, it is rolled outward from each 
margin, it is called revolute. 

It must be borne in mind that in botanical usage the inner 
surface of the leaf is that which, in the majority of flattened 







Fig. 32. 



Fig. 33. 



Fig. 34. 



Fig. 35. 



Fig. 32. — Young Fern leaf, illustrating circinate vernation. 

Fig. 33. — Young leaf of the Birch, illustrating plicate vernation. 

Fig. 34. — Transverse section of the young leaf of the common Violet, illus- 
trating involute vernation. 

Fig. 35. — Transverse section of the young leaf of Yellow Dock, illustrating 
revolute vernation. 

leaves, constitutes the upper surface when fully expanded; it is 

also called the ventral surface, and the outer is termed the dorsal. 

When considered with reference to each other, several distinct 




Fig. 36. 




Fig. 37. 




Fig. 38. 



Fig. 36. — Diagram illustrating equitant vernation. 

Fig. 37. — Diagram of half-equitant vernation. Leaves of Sage. 

Fig. 38. — Diagram of triquetrous vernation. Leaves of Sedge. 

forms of prefoliation are also observed: It is equitant when, as 
in the Iris, the leaves are conduplicate, and those exterior over- 
ride or straddle successively both margins of the ones next interior 



CHAPTER III. — THE LEAF. 



35 



to them, Fig. 36; it is called half-equitant when, as in the Sage, 
the leaves are conduplicate, and each leaf embraces or straddles 
only one margin of the other, Fig. 37; and it is said to be trique- 
trous when, as in the Sedges, Fig. 38, the leaves are conduplicate, 
and so arranged that the bud is triangular in cross-section. Other 
modes of the disposal of leaves with reference to each other will 
be considered under aestivation or prefloration, when we come to 
the study of the flower. 




Fig. 39. 



Fig. 40. Fig. 41 



Figs. 42 and 43. 



Fig. 44. 



Fig. 39. — Branch of Privet, showing the opposite and decussate leaves. 

Fig. 40. — Whorled leaves of the Canada Lily. 

Fig. 41. — Branch illustrating the alternate, V 2 or distichous arrangement of 
leaves. 

Fig. 42. — Portion of stem of Carex, with leaves partially cut away, showing 
the 1/3 or tristichous arrangement. 

Fig. 43. — Transverse section of leaves of Carex, showing tristichous arrange- 
ment. 

Fig. 44. — Branch showing 2/5 or pentastichous arrangement of leaves. 



Phyllotaxy. This term has reference to the arrangement of 
leaves on the stem. It is important to observe that they do not 
occur at random on a stem or branch, but in a definite order, 
although the order varies in different plants, and sometimes is 
different on different parts of the same plant. 

There are two general plans of phyllotaxy; first, the whorled 
or verticillate, and second, the alternate or scattered. 

In the whorled plan two or more leaves occur at a node or 
on the same level, as in Figs. 39 and 40. Where there are but 
two leaves at a node they are almost invariably situated 180° apart, 
that is, the circumference of the stem is equally divided between 
them, and the leaves are said to be opposite. 

Opposite leaves are usually decussate, that is, the second pair 



36 PART I. — ORGANOGRAPHY. 

stand over the intervals between the first pair, as in Fig. 39. Usu- 
ally, also, when there are three leaves in the whorl, they are 
one-third of the circumference of the stem apart; when four, one- 
fourth, and so on, and as a general rule also the leaves of successive 
whorls stand over the interspaces of those immediately below them. 
Good examples of opposite leaves are those of the Mints, Maples 
and Lilac, and of whorled leaves in which there are more than two 
leaves in the whorl, the Galiums, Canada Lily, Leptandra and 
Silene stellata afford good illustrations. 

In the alternate or scattered plan but one leaf occurs at a node, 
and the leaves succeed each other in a spiral order. 

This is much the more common mode of phyllotaxy, and a con- 
siderable number of different forms of it are recognized, the 
greater portion of which may be reduced to a series mathemati- 
cally represented by the fractions 1/2, 1/3, 2/5, 3/8, 5/13, etc. In 
these fractions the numerator represents the number of turns to 
complete a cycle, that is, to reach a leaf which stands directly 
above the first; the denominator represents the number of perpen- 
dicular rows of leaves on the stem, or, what is the same thing, the 
number of leaves, counting along the spiral from any one of them, 
to the one which stands directly above it; and the whole fraction 
expresses the angular distance measured circumferentially on the 
stem from one leaf to the next one on the spiral. 

It will be observed also that the third fraction of the series 
is derivable from the first two by adding together the numerators 
for a new numerator and the denominators for a new denominator ; 
that the fourth is derived from the second and third in the same 
way, and so on. 

Examples of the 1/2 or distichous arrangement occur in the Elm 
and Basswood, and it prevails in the whole family of Grasses; it 
is illustrated in Fig. 41. The 1/3 or tristichous arrangement occurs 
in the Sedges, as shown in Figs. 42 and 43; the 2/5 or pentasti- 
chous arrangement occurs in many common trees, as the Cherry 
and Apple, and is illustrated in Fig. 44; the 3/8 or octastichous 
arrangement is observed in Aconite, Osage Orange, Plantain and 
Holly; the more complex plans are rarer, but the 5/13 is observed 
in the Houseleek and some other plants, and arrangements repre- 
sented by this and fractions still higher in the series occur in the 
cones of various species of Pines, Spruces, etc. Even where the 
leaves are compactly clustered or fascicled, as in the Larch, Fig. 




CHAPTER III. — THE LEAP. 37 

45, and some other trees, careful examination reveals the fact 
that the arrangement is really a spiral one. 

It is not uncommonly the case, of course, that in a mature 
branch we find some slight deviations from regularity in the 
arrangement of leaves, but these are of such a character that they 
may readily be accounted for, either by the distortions which stems 
frequently undergo during the process of growth, or by the failure 
of some of the leaves to develop. 

It will be seen that since branches usually spring from axillary 
buds, their arrangement must also be regular and correspond in 
plan with that of the phyllotaxy. 

Duration of Leaves. Leaves differ widely as to their period 
of duration. They are described as persistent or evergreen, if they 
remain green and on the tree for a year or 
more; they are deciduous, if unfolding in 
the spring or summer, they fall off in the 
autumn or the season of frobts; and if fall- 
ing off early in the season, as is the case 
with bud-scales, and often also with other 
Fig. 45.--Po'rtion of twig imperfect leaves, they are described as 
feav^s rch ' Sh ° wing fascicled fugacious or caducous. 

As now in tropical regions evergreen trees are much the more 
common, while in our own climate they are rare, there is good 
reason to believe that in the warm ages of the world preceding 
the ice period, all trees were evergreens, and that our northern 
trees have become deciduous-leaved by gradual adaptation to the 
vicissitudes of the climate. 

Position. According to their place of insertion on the stem, 
leaves often differ from each other .considerably in form and 
appearance, and it is often, therefore, convenient to use special 
terms indicative of their position. Cauline leaves are those which 
are inserted on the main stem; rameal leaves are those borne on 
the branches ; radical leaves are those which spring from the basal 
portion of the stem at or just beneath the ground; seminal leaves 
or cotyledons are those which are borne by the embryo in the seed ; 
and floral leaves are the leaves of the flower. 

Parts and Structure of Leaves. A leaf, when complete, consists 
of three parts, the lamina or blade, the petiole or leaf-stalk, and 
two small blade-like bodies at the base of the petiole called the 
stipules. Such a leaf is seen in the Tulip-tree, and is illustrated in 
Fig. 46. Frequently some of these parts are wanting. The stipules, 



38 



PART I. — ORGANOGRAPHY. 



being least serviceable to the plant, are most frequently absent; in 
this case the leaf is described as exstipulate; not uncommonly the 




Fig. 46. — Leaf of Tulip-tree, illustrating 
the parts of a complete leaf. The upper 
part, a, is the lamina, and below is the 
petiole, b, at the base of which are the two 
stipules, c. 



petiole is wanting and the blade is inserted directly upon the stem; 
it is then described as sessile; sometimes the blade is not merely 





Fig. 47. — Part of stem of Uvularia, 
illustrating perfoliate leaves. 



Fig. 48. — Connate leaves of the 
Honeysuckle. 



sessile, but more or less embraces the stem at the base, when it is 
called clasping; sometimes it grows quite around the stem, and its 



CHAPTER III. — THE LEAF. 



39 



edges even coalesce on the opposite side, so that the stem appears 
to grow through its base as in the Bell-wort, Fig. 47, when it is 
described as perfoliate; sometimes, in the case of opposite leaves, 
the bases grow together or become coherent, apparently forming a 
single leaf, with its stem passing through its middle, as in the 
Cup-plant, the Boneset, and the Honeysuckle, Fig. 48, in which 
case they are called connate, and sometimes the margins of the 
leaf grow down the sides of the stem, or become decurrent, as in 
the Mullein, the Sneeze-weed and the Comfrey, Fig. 49. In some 
plants, the petiole of the leaf is swollen where it joins the stem, 
forming a leaf cushion or Pulvinus. 




Fig. 49 



Fi#. 49. — Decurrent leaf of Comfrey. 

Fig. 50. — Portion of stem of Lathyrus anhaca. one of the Pulse familv. 
showing stipules which perform the functions of a leaf-blade while the blade 
proper is developed into a tendril. 

The blade is commonly thought of as the leaf and the other 
parts as appendages, but even the blade, although the most impor- 
tant part, may be wanting or developed into some form different 
from the ordinary one, while either the stipules or the modified 
petiole performs its functions. Lathyrus aphaca, Fig. 50, is an 
example of a leaf in which the stipules become strongly developed 
and perform the functions of blades, while the petiole and blade 
proper are modified into a tendril for the purpose of enabling the 
plant to climb. 

In most of the Australian Acacias, trees which in other coun- 
tries are noted for their graceful, feathery foliage, both blade 
and stipules of all but the earlier leaves fail to develop, while the 
petiole becomes flattened and performs the functions of a blade. 
These flattened petioles, or phyllodia, as they are called, are simple, 



40 



PART I. — ORGANOGRAPHY. 



parallel-veined, and placed with their edges vertical; hence the 
Australian species present a widely different appearance from the 
nearly related ones of other countries. Fig. 51 represents one of 
the earlier leaves of one of these Acacias, showing a widened 
petiole, and the tendency to develop phyllodia, and Fig. 52 repre- 
sents a fully formed phyllodium of the same tree. 

It is frequently the case, however, that all parts may be pres- 




Fig. 51. 



Fig. 52. 



Fig. 51. — Leaf of an Australian Acacia, showing tendency to abortion of 
leaf-blade and the development of the petiole into a phyllode. 
Fig. 52. — Fully developed phyllode of an Australian Acacia. 



ent, but, owing to a change in their usual form, or a partial coales- 
cence with other parts, the presence of one or the other of them 
may be more or less obscured. In grasses, for example, the stipules 
appear to be united with the petiole to form the sheath which 
clasps or encloses the stem, but usually their apices are free and 
slightly project at the junction of the blade and sheath, forming 
what is called the ligule, Fig. 53. 

In the Polygonums the stipules cohere with each other, and 
form a sheath about the stem. This stipular sheath, which is 
usually membranous, and may or may not have a free portion, is 



CHAPTER III. — THE LEAF. 



41 



called the ochrea. Not infrequently also the stipules become adnate 
to the petiole, as in the Rose, Fig. 54, or become converted into 
spines, as in the Locust, Fig. 55, and in some instances they are 
changed into tendrils, as in the Green Briar, Fig. 56. In many 
instances also they are scaly, and after serving the purpose of 
protection in the bud, fall away when the leaves expand. 

Considering the structure of the parts of the leaf, we find the 
blade and stipules, when normally developed, consist of a tough 
framework or system of veins, which serves chiefly for support 
and partly to conduct the nutritive fluids; an intervening soft 
tissue called the mesophyll, or leaf-parenchyma, and an epidermis 





Fig. 54. 



Fig. 55. 



Fig. 53. — Leaf of grass, showing lamina, sheath and ligule. 

Fig. 54. — Adnate stipules of Rose. 

Fig. 55. — Stipules of the common Locust converted into spines. 



which covers the whole. The petiole consists more largely of 
fibrous tissue, the continuation of the framework of the blade, and 
possesses comparatively little parenchyma. 

The Venation of Leaves. By this is meant the arrangement of 
the veins or framework. In such simple leaves as many of the 
Mosses, no veins are present, and the leaf consists merely of a 
layer of green cells, but in higher plants a venation is always 
more or less distinctly recognizable. Three different types of it 
are distinguished: the furcate or forked venation, in which the 
veins fork or divide once or repeatedly into equal divisions, as 



42 



PART I.— ORGANOGRAPHY. 



seen in many ferns and other cryptogamous plants, but seldom in 
flowering plants, see Fig. 57; the parallel-veined plan, the common 
form observed in Monocotyledons, as Grasses, Palms, Lilies, etc.; 
and the reticulate, or net-veined plan, the type which prevails in 
Dicotyledonous plants, such as the Roses, Maples, Oaks, etc. 

Among parallel-veined leaves three different modifications are 
observed: (1) The type in which the veins run nearly parallel to 




Fig. 56. 





Fig. 58. 



Fig. 56. — Stipules of Green Briar (Smilax) developed into tendrils. 

Fig. 57. — Pinnule of Osmunda regalis, a Fern, illustrating furcate venation. 

Fig. 58. — The leaf of Gloriosa ; a basi-nerved leaf. 

each other from the base to the apex of the leaf. Such leaves 
incline to elongated forms, and are well illustrated in most grasses, 
and in the Gloriosa Lily, Fig. 58. (2) The type in which the veins 
are straight and radiate from the .petiole to the margin of the 
blade. Such leaves incline to rounded forms, as illustrated in the 
leaf of the Fan Palm, Fig. 59. (3) The type in which there is a 
mid-rib or vein running from the base to the apex of the leaf, and 
straight or somewhat curved veins running from this, nearly 
parallel to each other, to the margin, as seen in the Banana and 
the Calla Lily, Fig. 60. 

In the reticulate plan the veins branch repeatedly, and the 
veinlets, or small branches of different veins, run together end 



CHAPTER III. — THE LEAF. 



43 



to end, or anastomose, forming a more or less complicated net- 
work. There are also three modifications of this type: (1) The 




Fig. 59. — The leaf of a species of Palm; a "palmi-nerved" leaf. 

pinnately netted or feather veined, in which there is a mid-rib 
with lateral branches which run toward the margin, branching 
repeatedly and forming a network, as in Fig. 61; (2) the palmately 
or radiately netted, a reticulate leaf in which there are several ribs 




Fig. 60. 



Fig. 61. 



Fig. 62. 



Fig. 63. 



Fig. 60. — The leaf of the Calla ; a "pinni-nerved" leaf. 

Fig. 61. — The leaf of Carpinus ; a pinni-reticulate leaf. 

Fig. 62. — The leaf of the White Poplar; a palmi-reticulate leaf. 

Fig. 63. — The leaf of the Wild Yam ; a costate-reticulate leaf. 



44 



PART 



-ORGANOGRAPHY. 



radiating from the petiole to the margin, as in the leaf of the 
White Poplar, Fig. 62, and (3) the costate or ribbed-netted leaf, in 
which there are several prominent veins or ribs running from base 
to apex of the leaf, with a network of small veins between, as in 
the leaf of the Wild Yam, Fig. 63. The first and third varieties 
incline to elongated and the second to rounded forms, though there 
are some exceptions to the rule, 



The Shapes of Leaves. 

The shapes of leaves are very numerous, and as they often 
afford characters by means of which plants are distinguished, it is 
important for the student to be familiar with the more common 
forms and the terms used in describing them. For the most part 

leaves incline to bilaterally 
symmetrical forms, that is, the 
two sides of the leaf ar^ counter- 
parts of each other in size and 
shape, but it sometimes occurs, 
as in the Begonias, Fig. 64, that 
one side is much better devel- 
oped than the other. Such 
leaves are termed inequilateral. 
It not infrequently happens that 




Fig. 64. — Begonia leat, showing 
inequilateral shape. 



the bases of simple leaves and the leaflets of compound ores show 
a slight inequality. 

Simple Leaves. A simple leaf is one which has a single blade, 
which may either be sessile or petiolate, but if the latter, petiole 
and blade are united directly and not by means of a joint. We 
may conveniently describe simple leaves and the separate blades 
of compound leaves as to general outline, apex, base, marginal, 
indentations, surface and texture. 

(a) General Outline. By this we mean the outline form of 
the leaf, disregarding marginal indentations and slight irregular- 
ities. The principal forms are the linear, a narrow, elongated 
form, with parallel margins, as represented in Fig. 65; the oblong, 
which is broader, but considerably longer than wide, with sides 
nearly parallel and ends rounded, Fig. 66 ; the elliptical, somewhat 



CHAPTER III. THE LEAF. 



45 



longer than wide, with rounded ends and sides, Fig. 67: the oval, 
or broadly elliptical, Fig. 68; the lanceolate, or lance-shaped, Fig. 
69; the oblanceolate, or inversely-lance-shaped, Fig. 70; the ovate, 
which is shaped like the longitudinal section of a hen's egg, and 
has the petiole at the larger end, Fig. 71; the obovate, or inversely 
ovate, as in Fig. 72; the spatulate, which is larger and rounded at 



\i 



^ 



T 




Fig. 65. Fig. 66. Fig. 67. 



Fig. 68. Fig. 69. Fig. 70. Fig. 71. Fig. 72. 




Fig. 73 Fig 74. 



Fig. 75. 



Fig. 76. Fig. 77. 



Figs. 65 to 77, inclusive, diagrams illustrating shapes of leaves as respects 
general outline; 65, linear; 66, oblong; 67, elliptical; 68, oval; 69, lanceolate; 70. 
oblanceolate; 71, ovate; 72, obovate; 73, spatulate; 74, panduriform ; 75, orbic- 
ular; 76, ensiform ; 77, subulate. 



the apex, and tapering at the base like the old-fashioned spatula, 
Fig. 73; the panduriform, or fiddle-shaped, Fig. 74; the orbicular, 
which is nearly circular in outline, Fig. 75 ; the ensiform, or sword- 
shaped, as in the Iris, Fig. 76; the subulate, or awl-shaped, as the 
leaves of Arbor Vitae and Cedar, Fig. 77; and the filiform, or 
thread-shaped, proportionately very long and narrow, as the leaves 
of Asparagus. 

(b) The Apex. As regards the shape of the apex, the follow- 
ing are the more important forms: The obcordate, or inversely 



46 



PART I. — ORGANOGRAPHY. 



heart-shaped, Fig. 78; the emarginate, or notched, Fig. 79; the 
vetuse, with a broad, shallow sinus at the apex, Fig. 80; the aris- 
tate, with the apex terminating in a bristle, Fig. 81 ; the mucronate, 
with the apex terminating in an abrupt, soft point, Fig. 82; the 
cuspidate, the same as mucronate, but with a hard point; the 




Fig. 78. Fig. 79. Fig. 80. Fig. 81. Fig. 82. 



Fig. 84. Fig. 85. Fig. 86. 



Figs. 78 to 86, inclusive, diagrams illustrating forms of leaf apices ; 78, obcor- 
date ; 79, emarginate; 80, retuse ; 81, aristate ; 82, mucronate (or if the point be 
hard, cuspidate); 83, truncate; 84, obtuse; 85, acuminate; 86, acute. 

truncate, with the apex terminating abruptly, as if cut off, Fig. 83 ; 
the obtuse, with a rounded or blunt apex, Fig. 84; the acuminate, 
or taper-pointed, Fig. 85 ; and the acute, with an apex which forms 
an acute angle, Fig. 86. 




Figs. 87 



Figs. 87 to 95, inclusive, diagrams illustrating forms of leaf bases; 87, rounded 
or obtuse; 88, truncate; 89, cuneate ; 90, cordate; 91, sagittate; 92, hastate; 
93, auriculate ; 94, reniform ; and 95, peltate. 



(c) The Base. As respects the shape of the base the following 
are the most common forms : The rounded, or obtuse, Fig. 87 ; the 
truncate, Fig. 88; the cuneate, or wedge-shaped, Fig. 89; the cor- 
date, or heart-shaped, Fig. 90; the sagittate, or arrow-shaped, Fig. 
91; the hastate, or halberd-shaped, Fig. 92; the auriculate, when 
there are two ear-like appendages at the base, Fig. 93; reniform, 
or kidney-shaped, Fig. 94; and the peltate, or shield-shaped, where 
the petiole is attached near the center of the blade, as in Fig. 95. 

(d) Marginal Indentations. Here we may distinguish between 
indentations that are shallow, extending considerably less than half 
way to the mid-rib or to the base (if radially indented), and those 
which are deeper. 



CHAPTER III. — THE LEAF. 



47 



Among the more important forms with shallow indentations 
are the following: The serrate, or saw- toothed, with sharp teeth 




Fig. 99. 



Fig. 100. 



Fig. 101. 



Fig. 102. 



Figs. 96 to 102, inclusive, diagrams illustrating marginal indentations of 
leaves; 96, serrate, serrulate and bi-serrate ; 97, dentate, denticulate and bi- 
dentate ; 98, crenate, crenulate and bi-crenate ; 99, undulate, sinuate and repand ; 
100, crenate-dentate ; 101, spinose ; and 102, crispate. 




Fig. 103. Fig. 104. Fig. 105. Fig. 106. Fig. 107. 

Figs. 103 to 107, inclusive, diagrams illustrating the deeper marginal indenta- 
tions in pinnately-veined leaves; 103, runcinate ; 104, pinnately-lobed ; 105, pin- 
nately-cleft ; 106, pinnately-parted, and 107, pinnately-divided. 

which incline forward like the teeth of a hand-saw, the serrulate, 
or minutely saw-toothed, and the bi-serrate, or doubly serrate, 



48 PART I. — ORGANOGRAPHY. 

with two sets of teeth, one upon the other, see Fig. 96 j the dentate, 
or toothed with outwardly projecting teeth, the denticulate, or 
finely dentate, and the bi-dentate, or double-dentate (the three 
forms are illustrated in Fig. 97) ; the crenate, or scalloped, the 
crenulate, or minutely crenate, and the bi-crenate, or doubly-crenate 
(illustrated in Fig. 98) ; the undulate, or wavy; the sinuate, or 
deeply-wavy, and the repand, or undulate-dentate, with a margin 
like that of an umbrella, Fig. 99. Other forms are the crenate- 
dentate, or scalloped, with the scallops produced into sharp teeth, 
as in Fig. 100; the spinose, with the margin spiny, Fig. 101; the 
ciliate, with the margin fringed with hairs; the fimbriate, with the 
margin cut into slender segments or fringed, and the crispate, with 
the margin crisped, as in Fig. 102. 

The commoner forms with deeply indented margins, are the 
following: The incised is one in which the margin is jagged, or 
irregularly and rather deeply cut, as if cut with a knife. The 
peculiar form of pinnately-incised leaf observed in the Dandelion 
and some other Composite, Fig. 103, in which the teeth are re- 
curved, is called runcinate. The lobed is one in which the indenta- 
tions extend nearly half way to the mid-rib or base, and in which 
either the segments or sinuses, or both, are rounded as in the leaves 
of some Oaks, Fig. 104; the cleft is the same as the lobed, except 
that the sinuses are deeper and commonly acute, Fig. 105; the 
parted is one in which the incisions, of whatever form, extend 
nearly but not quite to the mid-rib, as in the leaf of the Poppy, 
Fig. 106; and the divided is one in which the incisions extend quite 
to the mid-rib, but the segments are unstalked, as in the leaf of 
the Cress, Fig. 107. 

It is evident that if the venation is pinnate, the series of forms 
may be described as pinnately-incised, -lobed, -cleft, -parted or 
-divided, as in the series of figures from 103 to 107 inclusive. If, 
however, the venation is radiate, as in the series of figures from 
108 to 112 inclusive, they will be described as radiately or pal- 
mately-incised, -lobed, etc. 

The terms pinnatilobate, pinnatifid, pinnatipartite and pinnati- 
sect are used synonymously with pinnately-lobed, pinnately-cleft, 
pinnately-parted and pinnately-divided, respectively. The corre- 
sponding terms descriptive of the radiate or palmate forms are 
palmatilobate, palmatifid, palmatipartite and palmatisect. 

The number of lobes, segments or divisions may be indicated 
by appropriate numerical prefixes, thus: Bilobate, trilobate, multi- 



CHAPTER III. — THE LEAF. 



49 



lobate; bifid, trifid, multifid; bipartite, tripartite, multipartite; 
bisect, trisect, multisect, etc.; and in case it is desired at the same 
time to indicate the arrangement of the segments or lobes, the 




Fig. li 



Fig. 110. 



Fig. 111. 



Fig. 112. 



Figs. 108 to 112, inclusive, diagrams illustrating the palmately-veined leaves 
with deep marginal indentations; 108, palmately-incised ; 109, palmately-lobed ; 
110, palmately-cleft ; 111, palmately-parted, and 112, palmately-divided. 

modifying adverbs pinnately and palmately, or radiately, may be 
used, as pinnately quadrifid, palmately multisect, radiately tri- 
lobate, etc. 

A leaf which is pinnately-parted in such a manner that the 
divisions are linear and stand'out from the axis, parallel to each 
other, as the teeth of a comb, is commonly described as pectinate, 





Fig. 113. 



Fig. 114. Fig. 115. 



Fig. 113. — Diagram illustrating pectinate leaf. 

Fig. 114. — Palmately-dissected leaf of the Yellow Water Ranunculus. 

Fig. 115. — Pinnately dissected leaf of Chamomile. 

see Fig. 113. Leaves which are separated into numerous irregu- 
larly branching divisions are described as dissected, and such 
leaves may be either palmately-dissected, as the submerged leaves 
of the Yellow Water Ranunculus, Fig. 114, or pinnately-dissected, 
as the leaves of Chamomile, Fig. 115. 

It not infrequently happens that the segments of a deeply in- 
dented leaf may again be incised, lobed, etc. Such forms, according 
to the depth of the incisions, and the arrangement of the segments, 
are described as bipinnatifid, bipinnatisect, bipalmatisect, etc. 



50 



PART I. — ORGANOGRAPHY. 



Compound Leaves. A compound leaf is one whose blade is 
divided into two or more distinct sub-divisions, called leaflets. 
These leaflets may possess stalks or petiolules of their own, and in 
many cases they are fastened to the main axis by means of a joint ; 
but frequently also the leaflets are sessile, that is, attached directly 
to the main axis. In case, however, the parenchyma of the leaflet 
is confluent with the axis it is regarded as a divided simple leaf, 
and not as a compound one. It will be seen, therefore, that the 
transition from simple to compound leaves is a very gradual one. 
As a matter of fact, in some instances it is difficult to say whether 
a given form should be regarded as simple or as compound. 

Since the compounding or branching of a leaf always follows 




Fig. 116. 



Fig. 117. Fig. 118. Fig. 119 



Fig. 121. 



Figs. 116 to 121, inclusive, forms of pinnately-compound leaves; 116, parf» 
pinnate; 117, impari-pinnate ; 118, cirrhosely pinnate; 119, interruptedly-pinnate ; 
J20, lyrate ; and 121, bi-pinnate. 



the plan of venation, we may have either pinnately or. radiately 
compound leaves. 

The following are the most important of the pinnate forms: 
The pari-pinnate, or abruptly pinnate, in which the leaf is 
terminated abruptly by a pair of leaflets, as in Fig. 116; the im- 
pari-pinnate, or odd-pinnate, in which the leaf terminates with ^ 
single leaflet," as in Fig. 117; the cirrhosely-pinnate, in which th0 
leaf is terminated by a tendril, as in Fig. 118; the interruptedly -> 
pinnate, in which, as in the Silver-weed and Potato, Fig. 119, ther^ 
are smaller leaflets scattered among larger ones; the lyrate, leaf, 
in which the terminal leaflet is largest, and the others successively 
smaller toward the base, as in Fig. 120, and the leaves that are 
more than once compounded on the pinnate plan. Fig. 121 showg 
a leaf which is twice compounded ; it is called a bi-pinnate leaf ; one 
which is three times compounded on the same plan is tri-pinnate; 
one that is many times pinnately compounded, multi-pinnate, and 



CHAPTER III. THE LEAF. 



51 



a leaf which is somewhat irregularly compounded many times on 
the pinnate plan is termed pinnately '-decompound. 

A similar series of terms apply to leaves compounded on the 
Tadiate plan. Such a leaf, compounded on the plan of three is a 
palmately-trif 'olio late or ternate leaf, as the leaf of the Clover, 
Fig. 122; one with four radiating leaflets is palmately-quadrif olio- 
late, or quadrate, as the leaf of Marsilea, Fig. 123; a radiate leaf 
with five leaflets is palmutely-quinquefoliolate, or quinate, Fig. 124, 
and the Horse-chestnut furnishes an example, Fig. 126, of a pal- 
mat ely -sept emfoliolate or septenate leaf, while the Lupine and 
some other plants produce palmate leaves with a still larger num- 
ber of leaflets. There are also biternate, triternate, multiternate 
and ternat ely -decompound leaves. Fig. 125 is an example of a 
biternate leaf. The primary divisions of a compound leaf are 
termed pinnae, the divisions of the pinnae are termed pinnules and 
the ultimate divisions or little blades are termed leaflets. 

Leaf Surface. In the observation and description of leaves and 
other portions of the plant body, it is often important to take into 
account the character of the surface. 

Plant surfaces are glabrous, when smooth, or free from hairs 
or protuberances of any kind ; glaucous, when covered with a bloom, 
as the leaf of the Cabbage; punctate, when dotted with pellucid or 
other dots ; glandular, when bearing glands or secreting vesicles on 
the surface ; rugos.e T when wrinkled ; scabrous, when harsh or rough 




Fig. 126. 

Figs. 122 to 126, inclusive, forms of palmately-compound leaves; 122, ternate; 
123, quadrate; 124, quinate; 125, bi-ternate ; and 126, septenate. 

to the touch ; verrucose, when covered with protuberances or warts ; 
pubescent, when covered with rather short, soft hairs; puberulent, 
when minutely pubescent; sericeous, when covered with a pubes- 
cence of very fine, appressed, silky hairs ; lanuginous, when covered 
with wooly hairs; tomentose, when covered with matted or felted 
hairs; villose, when bearing long, soft, shaggy hairs; pilose, when 



52 



PART I. — ORGANOGRAPHY. 



bearing long, straight, soft hairs ; floccose, when bearing tufted, or 
cottony hairs ; hispid, when covered with stiff hairs or bristles ; 
strigose, when covered with stout, sharp, appressed hairs; spinose, 
when provided with spines; echinate, when possessing barbed 
prickles; and aculeate, when prickly. 

Texture of Leaves. It is also of some importance to observe 
the texture or consistence of leaves. They are described as mem- 
branous, when thin and pliable; as succulent, when thickened and 
juicy, as the leaves of Live-for-ever, etc.; as scarious, when dry, 
like bud-scales; as coriaceous, when thickish and leathery, like the 
leaves of the great-flowered Magnolia; as herbaceous, when green 
in color, as most ordinary leaves ; and as petaloid, when colored 
like petals, or of some lively color other than green. 

Specially Modified Leaves. Some of these, such as bud-scales 
and leaf -tendrils, have already been mentioned, but there are many 
others which, having become adapted to functions altogether dif- 
ferent from ordinary foliage, have also acquired forms which in 




Fig. 127. — Leaf of Vetch with upper leaflets developed into tendrils. 

Fig. 128. — Leaf of Lathyrus aphaca,- with the leaf-blade and petiole developed 
into a tendril, while the functions of leaf-blade are discharged by the stipules. 

Fig. 129. — Leaf of a Smilax, with the stipules developed into tendrils. 

Fig. 130. — Leaf of a species of Clematis with petiole serving the function of 
a climbing organ. 



some instances only remotely resemble those of foliage-leaves. The 
scales of bulbs like those of the Garlic and Lily, and of bulblets 
like those of some varieties of the Onion, are only leaves surcharged 
with nutriment stored up to enable the plant to accomplish a vigor- 
ous growth during the succeeding season; the spines into which 
some of the leaves of the Barberry and all of those of most species 
of Cactus are changed, subserve protective purposes, effectually 
defending the plants against browsing animals, and the upper 
leaflets of the common Pea and Vetch, Fig. 127, the entire blade 



CHAPTER III. — THE LEAF. 



53 



and petiole of Lathyrus aphaca, Fig. 128, and the stipules of a 
Smilax, Fig. 129, are modified into tendrils, and serve the purpose 
of climbing organs. 

Sometimes the petioles, while performing the ordinary func- 
tion of supporting the blade, also become sensitive or irritable to 
the touch the same as tendrils, and like them perform the func- 
tions of climbing organs, as in the Clematis, Fig. 130, and Solanum 




zMtps^- 




Fig. 131. 




Fig. 132. 



Fig. 131. — Leaf of the Sundew serving the purpose of an insect trap. 

Fig. 132. — Leaf of Venus' Fly-trap. 

Fig. 133. — Leaf of the Northern Pitcher-plant (Sarracenia). 

Fig. 134. — Leaf of the California Pitcher-plant (Darlingtonia). 

jasminoides, already referred to, Fig. 18; and sometimes they are 
developed into insect traps of various forms, as in the Sundew, 
Venus' Fly Trap, the various Pitcher-plants, etc. 

Fig. 131 represents the leaf of the common Sundew. The hairs 
or tentacles distributed over the surface are each tipped with a 
pellucid drop of sticky material, by means of which small insects 
which alight on the leaf are secured; the tentacles all then bend 
over upon the insect, and the leaf itself partially rolls inward so 
as to envelop him, and by means of a secretion akin to gastric 
juice, which the secreting glands of the tentacles pour out freely 
upon the doomed animal, the nutritive portions of his body are 
dissolved and gradually absorbed by the plant as food. 

Fig. 132 represents one of the rosette of radical leaves of the 
Venus Fly-trap, a plant belonging to the same family as the Sun- 
dew. The blade of the leaf consists of two spiny-margined valves, 
which are movable upon the mid-rib as upon a hinge. The face of 
each valve is also provided with three sensitive spines, and when 
an insect, attracted by the glandular secretions on the surface of 
the lobes, alights on one of them and touches one of the sensitive 



54 PART I. — ORGANOGRAPHY. 

spines, the lobes instantly come together like the jaws of a steel 
trap, almost invariably securing the intruder, which becomes the 
food of the plant, and is digested in much the same way as is done 
by the Sundew. 

The leaves of the Pitcher-plant of our northern bogs, Sarracenia 
purpurea, Fig. 133, also entraps insects, though in a quite different 
way, and uses them for food. The pitchers are usually found from 
half to two-thirds filled with water, which is mainly secreted by the 
plant; the lip of the pitcher has its inner surface clothed with stiff 
and sharp-pointed bristles, which point downward, and a secretion, 
enticing to insects, is poured out on the inner surface, particularly 
about the throat. Insects are thus enticed into the pitchers in 
great numbers, and owing to the difficulty of getting past the 
sharp-pointed hairs, they seldom escape, but are drowned in the 
water within the pitcher, and their decaying 
bodies form a rich manure which goes to sus- 
tain the life of the plant. The leaves of Dar- 
lingtonia, Fig. 134, a related plant of Cali- 
fornia, catch insects in much the same way, 
and make the same use of them. And the 
East Indian Pitcher-plant, Nepenthes, Fig. 
135, has a leaf, the lower part of which serves 
as a blade, performing the proper functions of 
a foliage leaf; the middle portion is developed 
into a tendril, by means of which the plant 

Fig. 135.— Leaf of the ' J * 

East Indian Pitcher- climbs, and the apical portion is developed into 

plant (Nepenthes). 

a pitcher which, like that of Sarracenia, 
entraps insects which are then digested by the watery secretion 
and thus utilized for food. 

There are several other plants also which possess insectivorous 
habits, and whose leaves are modified more or less with reference 
to these habits; among them are the Bladder- worts, which develop 
little, bladder-like crustacean traps on their leaves; the Pinguicu- 
las, whose leaves are glandular on the upper surface, and which 
entrap and devour insects somewhat after the manner of the Sun- 
dew, though in a ruder fashion, and the Australian Cephalotus, 
which bears among its ordinary leaves others in the form of very 
perfect pitchers. 




CHAPTER IV. — THE BRANCHING OF ORGANS. 55 



Practical Exercises. 

1. Compare the following leaf forms and note their resemblances and dif- 
ferences: The scales of a Hickory bud, the fleshy scales of a Lily bulb, the 
large spines on the Prickly-pear Cactus, the different forms of leaves on the 
Barberry, the leaves of the Pitcher-plant, the petals of the Rose, and the leaf 
of the Maple. 

2. Determine what organs are represented, respectively, by the tendrils of 
the Grape, the thorns of the Plum, the flattened joints of the Prickly-Pear 
Cactus, and the pods of the Pea. 

3. Describe the following simple leaves as to their venation, the parts 
present, general outline, apex. base, margin, surface and texture, using the 
correct botanical terms: Those of the White Oak, Stramonium, Hard Maple, 
Birch, House Ivy, Solomon's Seal, Onion, White Pine, Timothy Grass, and 
Live-for-ever. 

4. Describe the following compound leaves as to the parts present, the 
plan of compounding, the number of leaflets and the general outline, apex, base, 
margin, surface and texture of the leaflets, using the descriptive language of 
botany: Those of the Pea, the Hemp, Sweet Clover, Common Field-Clover, 
Meadow-Rue, Locust, Honey-Locust, and Ash . 

5. Describe the Phyllotaxy of the Locust, of the Sycamore, of the Crab- 
Apple, of the Common Milk-Weed, of the Elm, of the Canada Lily, of the Flax, 
and of the White Pine. 

6. Examine the buds or unfolding leaves of the following plants and deter- 
mine the vernation : The Hickory, the Custard Apple, the Sweet Flag, the House 
Geranium, the Oak, the Sycamore, the Plantain, the Maple, the Common Poly- 
pody and the Ash. 



CHAPTER IV.— THE BRANCHING OF ORGANS. 

Not only stems but any organ of the plant-body may branch, 
and the branching is always according to one or other of two gen- 
eral types, the Dichotomous or the Monopodial. In the former 
mode the branching takes place by forking, or by the repeated 
division of the apex of the organ into two equal portions, as illus- 
trated in Fig. 136. Three different varieties of this mode are 
observed. 

(1) The Forked or Bifurcating Dichotomy, in which the 
branches develop equally, as in Fig. 136; 

(2) The Helicoid Dichotomy, in which the branch on one side 
is invariably suppressed, or less strongly developed than the other, 
as illustrated in Fig. 137; and 

(3) The Scorpoid Dichotomy, in which a branch is suppressed, 
or but partially developed, first on one side and then on the other, 
as in Fig. 138. 

This plan and its various modifications are more commonly 
seen in flowerless than in flowering plants. It is the common mode 
of branching in Marine Algae, the leaves of some Ferns, and in the 
stems and roots of Club-Mosses. 

In the monopodial type the branches originate as lateral out- 



56 



PART I. — ORGANOGRAPHY. 



growths, back of the apex of the main stem, as illustrated in Fig. 
139. There are also several modifications of this type : 




H V 



Fig. 138. 



Fig. 136. — Diagram of forked dichotomy. 
Fig. 137. — Diagram of helicoid dichotomy. 
Fig. 138. — Diagram of scorpioid dichotomy. 

(1) The Racemose Monopodium, in which the main axis re- 
tains the ascendency over its branches, as in Fig. 139. 

(2) The Cymose Monopodium, in which the main axis is soon 



N 



$ 



t 



Fig. 139. 





Fig. 141. 



Fig. 142. 



Fig. 139. — -Diagram of a racemose monopodium. 

Fig. 140. — Diagram of false dichotomy. 

Fig. 141. — Diagram of the helicoid monopodium. 

Fig. 142. — Diagram of the scorpioid monopodium. 

suppressed and the lateral branches gain the ascendancy. Of the 
latter kind there are several variations: 

(a) The False Dichotomy, represented in Fig. 140, in which 
the lateral branches develop in such a manner as to resemble true 
forks, or a genuine dichotomy. 

(b) The Helicoid Monopodium, in which the main axis and 
lateral branches on one side are habitually suppressed, while the 



CHAPTER IV. — THE BRANCHING OF ORGANS. 57 

branches on the other side are developed to form a false axis, as 
in Fig. 141. 

(c) The Scorpioid Monopodium, in which the main axis soon 
ceases to grow and the branches are suppressed alternately on 
one side and then on the other, as illustrated in Fig. 142. 

The monopodial type of branching is the one seen in the stems 
of Mosses, in both the roots and stems of Equisetums, in the roots, 
and sometimes in the leaves of Ferns, and in the stems, roots and 
leaves of nearly all flowering plants. 

Practical Exercises. 

Study carefully, as examples of the various modes of branching, the follow- 
ing, making diagrams of each: (1) The common Liverwort, Marchant-ia poly- 
morpha, as an illustration of forked dichotomy; (2) the larger branches of the 
common Maidenhair Fern, Adiantum pedatum, as illustrating helicoid dichotomy ; 
(3) the smaller branches of the same plant, as illustrative of Scorpioid dicho- 
tomy; (4) the trunk and branches of the Balsam Fir, as illustrating a racemose 
Monopodium; (5) the branching of the Lilac and Mistletoe, as illustrating the 
false dichotomy; (6) the arrangement of the flower clusters of the common Day 
Lily, as illustrative of the helicoid Monopodiiim, and (7) the flower clusters of 
the Sundew, as typical of the scorpioid Monopodium. 

The student should bear in mind that while in these examples the different 
modes of branching are clearly illustrated, it is not always equally easy to 
determine the plan, but sometimes a careful microscopical study of the branches 
in an early stage of their development is necessary, 



58 PART I. — ORGANOGRAPHY. 

CHAPTER V. 
THE ORGANS OF REPRODUCTION. 



Introductory. — Nature of the Flower. 

The organs for reproduction in phsenogamous or flowering plants 
consist of floiver, fruit and seed. They constitute a mechanism, 
more or less complex, whose function it is to continue the species. 
To this end, each part of the mechanism is subservient, and each, 
therefore, has a meaning which we should endeavor to understand. 
No part of it is so minute or apparently insignificant as not to 
deserve careful attention and thorough study. The organs of 
reproduction are not only interesting in themselves, inasmuch as 
flowers make strong appeals to everyone's sense of the beautiful, 
and inevitably awaken in thinking minds a desire to understand 
their structure, but they also furnish us with the most reliable 
characters for determining how nearly or how remotely different 
plants are related to each other; in other words, for classifying 
them according to their natural relationships. 

Perhaps nothing in the vegetable world is more wonderful than 
the immense variety of flowers. But this multiplicity of forms has 
not always existed. A careful study of the flora of the past, as 
revealed in its fossil forms, and a discriminating study of the 
plants of our own time, necessitates the conclusion that all this 
variety and complexity have arisen from comparatively few and 
simple forms. Progressive adaptation to environment has been 
the law of vegetable life. Plants have been subject to changing 
conditions of soil and climate. The earth's crust has been slowly 
elevated in some localities, and depressed in others; large areas 
of land have been alternately raised above the sea level and then 
submerged; these things have necessitated profound changes in 
temperature, in atmospheric humidity, and in other conditions 
affecting plant growth. Moreover, plants maintain a continual 
struggle with each other for the occupancy of the soil — a struggle 
whose conditions vary, not only with the changing physical condi- 
tions in the same locality, but with the dispersal of plants by 
various natural agencies to new localities, bringing them into asso- 
ciation with new plants and with new animal friends and foes. 
All these changes, necessitating changes in the habits of plants, 
taken in connection with the well-known tendency of plants to 



CHAPTER V. — THE NATURE OF THE FLOWER. 59 

vary, have led to profound modifications in their structure. The 
descendants of plants which were alike have come to differ from 
each other and from the parental forms; from a few kinds, an 
immense number of species and varieties have arisen. 

In the course of the adaptive changes which plants have under- 
gone, the organs of reproduction have, of course, also undergone 
much modification; but here conservatism is more evident, espe- 
cially as respects the essential organs of the flower, and changes 
in them have taken place more gradually than in other parts of 
the plant. The habits and appearance of related plants may have 
undergone profound change, while the flowers still bear a strong 
resemblance to each other in essential points of structure. The 
Elm and the Nettle, for example, are as different as possible from 
each other in size and in habits of growth, yet the record of their 
close relationship is preserved in their flowers. 

It is for these reasons — because of the light which flowers 
throw on the relationships of plants, and the clews they give us to 
the history of their descent — even more than on account of the 
appeal which beautiful flowers make to the aesthetic sense, that 
they command the enthusiastic interest of botanists. 

It must not be inferred from this, however, that the scientific 
study of a flower in any way dulls the enjoyment of it as a thing 
of beauty. It is a foolish, though popular, error to suppose that 
such is the case. It would be scarcely less absurd to suppose that 
the less one knows of art, the more he will enjoy a fine picture or 
a fine statue. Surely, in the study of flowers, as in every other 
subject worthy of knowledge, our enjoyment of them will increase 
as we understand them, and it will be measured by the extent and 
thoroughness of our knowledge of them. 

The older botanists considered the parts of the flower as having 
been derived from assimilative leaves through modifications or 
metamorphoses. This assumption was even carried to the extreme 
of ascribing the origin of ovules to the altered edges, perhaps 
teeth, of green leaves. In support of this hypothesis, it was argued 
that, first, the floral parts occur on the stem in the same order as 
leaves, and develop from it in the same way; second, that in the 
earliest stages of their growth, they are indistinguishable from 
true leaves in the corresponding stage of development; third, that, 
sometimes, when mature, they present every gradation from 
ordinary foliage, through bracts and sepals to petals and stamens; 
and fourth, that instances are known of abnormal or monstrous 



60 PART I. — ORGANOGRAPHY. 

flowers, where some or all of the floral organs appear to have re- 
verted to the condition of ordinary green leaves. 

However, during recent years it has been clearly established 
that, at least, ovules and pollen grains are not modified parts of 
any of the vegetative organs but can be traced through long 
descent from ancestral but independent structures in the lower 
plants. 

Nature of the Flower. A flower consists, then, of a leafy branch 
highly modified for the purposes of reproduction. Nature has de- 
veloped the form, and commonly also, the color of its parts, to suit 
the requirements of the reproductive process. The flower exists 
solely for the purpose of producing the seed. To this object its 
entire mechanism, and even the beauty of its corolla, its perfume 
and its nectar, are subservient. Even the vegetative processes of 
the plant, which precede the flowering, have largely for their object 
the storage of the energy necessary to enable the plant to produce 
its flower and develop its seed. In many cases, from that time the 
growth of the plant ceases. During the formation of the flower 
and the subsequent process of perfecting the seed, its stored-up 
energies suffer heavy drainage, resulting either in the death of the 
plant, as in the case of annuals, biennials and some perennials, or 
in its entering upon a period of rest to recuperate its exhausted 
vitality. 

Let us begin our study of flowers by observing their anthotaxy. 



CHAPTER VI.— ANTHOTAXY. 

By Anthotaxy is meant the arrangement of the flowers on the 
stem. It is often called inflorescence. Flowers may occur singly 
on the stem, or in clusters, and the latter may have various shapes 
and characteristic modes of arrangement. 

In a flower-cluster, the axis along which the flowers are ar- 
ranged is called the rachis, or axis of inflorescence; the common 
stalk of the cluster, the peduncle; the stalks of the individual flow- 
ers, the pedicels', and the modified leaves from which the branches 
of the cluster spring, bracts or bractlets, according as they occur 
on the rachis or on some of its branches. See Fig. 143. A leafless 
or nearly leafless stem or peduncle arising from an underground 
stem and bearing a flower or flower cluster is called a scape. 

Since flowers are modified branches and originate from buds 



CHAPTER VI. — ANTHOTAXY. 



61 



as do other branches, they follow the arrangement of buds, that is, 
they are either terminal or axillary, thus giving rise to two distinct 
types of Anthotaxy, the indeterminate, spikose or axillary type, 
and the determinate, cymose or terminal type. 




Fig. 143. — A raceme, showing 
axis of inflorescence, or rachis, 
a ; peduncle, b ; bracts, c ; ped- 
icels, d ; bractlets, e ; and flow- 
ers, f. 




Fig. 144. — Pimpernel, showing 
solitary indeterminate 
inflorescence. 



An Indeterminate or Ascending Anthotaxy is one in which the 
flowers occur in succession from the base toward the apex of the 




Fig. 145. — Corymb of a species of Cherry Fig. 146. — Umbel of a species of Onion. 

main stem. When clustered on this plan, those flowers come into 
blossom first which are situated lowest down on the rachis, or, in 



62 



PART I. — ORGANOGRAPHY 



the case of a flat-topped cluster, at the periphery. The principal 
forms of this type are the following: 

(1) The Solitary Indeterminate is one in which the flowers 
occur singly in the axils of ordinary leaves, as in the common Pim- 
pernel, Fig. 144. 

(2) The Raceme is a cluster in which the flowers are pedi- 
celled and occur in succession along a lengthened axis, blossoming 
from the base toward the apex, as in Fig. 143. Examples occur in 
the Choke-cherry and in the Currant. 

(3) The Corymb is like a raceme, except that it has the rachis 
proportionately shorter, and the lower pedicels somewhat length- 




Fig. 148. 



Fig. 147. — Spike of Plantain. 

Fig. 148.— Catkin of Birch. 

Fig. 149. — Head of Mimosa pudica. 



Fig. 149. 



ened so as to bring all the flowers to about the same level, as in 
Fig. 145, which represents the inflorescence of another species of 
Cherry. 

(4) The Umbel resembles a raceme, but has the rachis re- 
duced still more than in the corymb, and the nearly equal pedicels 
radiate from it like the rays of an umbrella, as in some species of 
Onion, Fig. 146. 

(5) The Spike is like a raceme, except that the flowers are 



CHAPTER VI. — ANTHOTAXY. 



63 



sessile instead of pedicelled. Examples occur in the wild Vervains 
and in the common door-yard Plantain, Fig. 147. 

(6) The Catkin, or Ament, is similar to the Spike, having its 
flowers sessile along a lengthened axis, but it differs from the latter 
in the fact that it has scaly instead of herbaceous bracts, as the 
clusters of staminate flowers of the Oak, Chestnut, Hazel and 
Birch, Fig. 148. 

(7) The Head or Capitulum is like a Spike, except that it has 
the rachis shortened so as to form a very compact cluster of sessile, 
or nearly sessile, flowers, as in the Clover, Button-bush and Mimosa, 
Fig. 149. A form of the Head characteristic of the great family 
Composite : s known as the Anthodium and simulates a simple 





Fig. 151. 



Fig. 150.— Head of Daisy. 
Fig. 151.— Strobile of Hop. 



flower, the ligulate ray flowers resembling a corolla, the involucre 
of green bracts resembling a calyx and the small and usually yel- 
low disk flowers having the appearance of stamens, see Fig. 150. 

(8) The Strobile is a compact cluster with large scales con- 
cealing the flowers, as in the inflorescence of the Hop, Fig. 151. 

(9) The Spadix is a flower-cluster like a spike (or sometimes 
shortened into a head) that is partially or wholly enclosed in a 
large bract called a spathe, which springs from its base. The 



64 



PART I. — ORGANOGRAPHY. 



inflorescence of the common Calla, the Skunk cabbage and the 
Indian turnip, Fig. 152, are illustrations. 

Several of the forms above described may be more or less com- 
pounded. For example, there are compound racemes, compound 




Fig. 154. — Compound umbel 
of Fennel. 



Fig. 152. — Spadix of 
Indian turnip. 



Fig. 153.— Panicle of Yucca. 

corymbs, compound umbels, and compound or panicled spikes. The 
compound raceme, particularly if it is somewhat irregularly com- 
pounded, is commonly called a panicle, as in the Yucca, Fig. 153. 
Fig. 154 illustrates the compound umbel of Fennel, and Fig. 155, 
the panicled spikelets of the Oat. 

The bracts which subtend the heads of the Composite, and those 
which occur in whorls at the base of other compact flower-clusters, 
as the umbels of many Umbelliferae, as well as the whorl of bracts 
which sometimes occurs beneath a single flower, as in the Anemone, 
are termed the involucre. 

A Determinate or Descending Anthotaxy is one in which the 
first flower that opens is the terminal one on the rachis, and the 
others appear in succession from the apex toward the base. In 
case the cluster on this plan is flat-topped, the flowering begins at 
the center instead of at the periphery, consequently the inflores- 
cence is often described as centrifugal, in distinction from the inde- 
terminate form, which is described as centripetal. 



CHAPTER VI. — ANTHOTAXY. 



65 



The principal varieties of determinate anthotaxy are the fol- 
lowing: 

(1) The Solitary Determinate is one in which there is a single 
flower at the end of the stem, as in the Wood Anemone, Fig. 156. 

(2) The Cyme is a loose cluster on the determinate plan, such 
as that illustrated in Fig. 157, which represents the inflorescence 




Fig. 155. Fig. 156. 

Fig. 155. — Panicled spikelets of the Oat. 
Fig. 156. — The Wood Anemone, illustrating solitary determinate inflorescence. 

of a species of Cerastium. A diffuse and freely branching cyme, 
like that of the common Elder and the Viburnums, is frequently 
called a Compound Cyme, and when such a cyme has shortened 
pedicels and is compactly arranged, as in the inflorescence of the 
garden Sweet William, it is termed a Fascicle. 

(3) A Glomerule or glomerulus, is a dense cluster on the 
cymose plan, whose flowers are sessile, or nearly so, on a short 
rachis. It resembles a head, but differs from it in the fact that 
the inflorescence is centrifugal. The Flowering and Canada Dog- 
woods both illustrate this form of inflorescence. See Fig. 158. The 
flower-cluster, as will be seen, is subtended by four conspicuous 



66 



PART I. — ORGANOGRAPHY. 



bracts, constituting an involucre; a represents one of the florets of 
the cluster magnified. 

A Scorpioid Cyme is one that imitates a raceme in appearance, 




Fig. 158. 



Fig. 157. 



Fig. 159. 



Fig. 157. — Open cyme of a species of Cerastium. 
Fig. 158. — Glomerule of the Canada Dogwood. 
Fig. 159. — Diagram of Scorpioid Cyme. 



having the flowers pedicelled and arranged along a lengthened axis. 
As in the raceme, the basal flower of the cluster is the oldest, but 
it is in reality terminal instead of axillary, as shown in the dia- 
gram, Fig. 159. Such an inflorescence arises either from the sup- 



CHAPTER VI. — ANTHOTAXY. 



67 



pression of all the branches on one side, in which case it would 
properly be called helicoid, or from the alternate suppression of 
branches, first on one side and then on the other, when it would 
be, in the strict sense, scorpioid. Owing, however, to the difficulty 
of distinguishing the two varieties when mature, they are indis- 
criminately called scorpioid cymes. Such cymes are commonly 





Fig. 160. — Scorpioid Cyme, or false raceme 
of Forget-me-not. 

Fig. 161. — Inflorescence of Peppermint, 
illustrating spiked verticillasters. 



Fig. 160 



one-sided or coiled in form. They are illustrated in the Sundew, 
the Heliotrope and the Forget-me-not, Fig. 160. Cymes of this 
kind also, not uncommonly branch into compound forms. 

(5) A Verticillaster is a compact cymose flower-cluster, which 
at first sight appears like a whorl or circle of flowers about a stem, 
but which in reality consists of two glomerules situated in the axils 
of opposite leaves. Clusters of this kind are seen in the Catnip, 



68 



PART I. — ORGANOGRAPHY. 



Horehound, Peppermint and other plants belonging to the natural 
order Labiatae, Fig. 161. 

A Mixed Anthotaxy is one in which the indeterminate and deter- 
minate plans are combined. Illustrations of this kind occur in 
many of the Composite where the heads of flowers, which of course 
are indeterminate clusters, are arranged in cymes. In the mints, 
on the contrary, verticillasters or cymose clusters are often ar- 
ranged in spikes, as seen in the Peppermint, Fig. 161. 

Mixed panicles are of very common occurrence, in fact more 
common than the purely indeterminate forms. They may be of 
two kinds, either the primary ramifications may be indeterminate 
and the secondary or ultimate ones determinate, or the latter may 
be indeterminate while the former are determinate. A somewhat 
elongated, profusely branching and compact luster of the former 
sort, like the inflorescence of the Lilac and Horsechestnut, is com- 
monly called a thyrsus or thyrse, 



Anthotaxy 

or 

Inflorescence. 



Indeterminate 
or 
Spikose. 



Determinate 

or 

Cymose. 



Mixed. 



Recapitulation. 



Solitary. 

Raceme. 

Corymb. 

Umbel. 

Spike. 

Catkin or Ament. 

Capitulum or Head. 

Strobile. 

Spadix. 

Compound Raceme, 



Corymb, Umbel, etc. 



Solitary. 

Cyme (proper). 

Compound Cyme. 

Fascicle. 

Glomerule. 

Scorpioid Cyme. 

Verticillaster. 



Mixed Panicle. 
Thyrsus or Thyrse. 
[ Spiked Verticillaster, etc. 



Practical Exercises. 



Determine whether the following inflorescences are indeterminate, determinate 
or mixed, and give the particular names applicable to each : The Currant, the 
Carrot, the Mustard, the Sycamore, the Red-ozier Dogwood, the Willow, the 
Frost Grape, the Wheat, the Potato, the common Milk-weed, the Hydrangea, the 
Burdock and the Harebell. 



CHAPTER VII. — PREFLORATION. 



69 



CHAPTER VII.— PREFLORATION OR ESTIVATION. 

By prefloration or aestivation is meant the arrangement of the 
floral organs, particularly calyx and corolla, in the bud. Since 
these parts of flowers are modified leaves, and flower-buds are 
structurally similar to leaf-buds, it is not strange that most of 
the terms explained under the head of prefoliation or vernation 
are applicable also to the arrangement of the floral organs in the 




Fig. 162. Fig. 163. 

Fig. 162. — Diagram or plan of flower of common Basswood. 
Fig. 163. — Diagram of induplicate-valvate prefloration. 

bud. These terms need not again be defined, but a few additional 
forms will be described, all of them relating to the arrangement of 
the organs with reference to each other. 

(1) The Valvate Prefloration. In this, the margins of adjacent 
members are contiguous merely, that is, do not at all overlap in 




Fig. 164. 



Fig. 165. 



Fig. 164. — Diagram of reduplicate-valvate prefloration. 
Fig. 165. — Diagram of involute-valvate prefloration. 

the bud. It is seen in its simplest form in the calyx of the Bass- 
wood flower, a ground plan of which is shown in Fig. 162. Of this 
form there are three other modifications: the induplicate-valvate, 
in which the edges of contiguous organs are bent inward, as in 



70 



PART 



-ORGANOGRAPHY. 



Fig. 163; the reduplicate-valvate, in which the edges are bent out- 
ward, as in Fig. 164; and the involute-valvate, in which the edges 
are rolled inward, Fig. 165. 

(2) The Imbricate Prefloration. Here the margins of adjacent 
parts overlap something like shingles on a roof. Of this, also, 
there are several modifications. The equitant and half-equitant 
have already been described. 




Fig. 166. 



Fig. 167. 



Fig. 168. 



Fig. 166. — Diagram. The outer whorl represents imbricate, the inner one, 
contorted prefloration. 

Fig. 167. — Diagram of plicate prefloration of the Harebell. 
Fig. 168. — Diagram of supervolute prefloration of Stramonium. 



(3) The Contorted Prefloration is that in which the parts are 
arranged with one edge invariably exterior and the other interior, 
giving to the bud a twisted appearance, as in the inner whorl, 
Fig. 166. 

(4) The Plicate or Plaited Prefloration. These terms, except 
when applied to the folding of a single leaf or floral organ, have 
reference only to those corollas or calyxes whose pieces are united. 
Such an organ folded lengthwise is called plicate, as the corolla 
of the Harebell, Fig. 167. In case the organ is both folded and 
twisted, as in the corolla of Stramonium, Fig. 168, it is commonly 
called supervolute. 



CHAPTER VIII.— THE STRUCTURE OF THE FLOWER. 



71 



Recapitulation. 



Prefoliatioii 

and 
Prefloration. 



Individual 
Leaf. 



Relative 
Arrangement. 



Inflexed or reclinate. 

Conduplicate. 

Convolute. 

Circinate. 

Plicate. 

Involute. 

Revolute. 



Valvate 
Series. 



Imbricate 
Series. 



16. Contorted. 



9. 
10. 

11. 

12. 
13. 
14. 
15. 



Calyx or Corolla I 17. 
when Parts are -s 



Plicate. 



Valvate. 

Induplicate- valvate. 
Reduplicate-valvate. 
Involute- valvate. 

Imbricate. 
Equitant. 
Half-equitant. 
Triquetrous. 



United. 



18. Supervolute. 



Practical Exercises. 

Examine the flower-buds of the following plants with reference to the pre- 
floration of calyx and corolla ; draw a diagram of the arrangement in each case, 
and apply to each the proper term descriptive of the prefloration : The Apple, 
the Mustard, the field Clover, the Morning-glory, the Butter-cup, the Geranium, 
the Buckthorn, the Grape and the Stramonium. 



CHAPTER VIII.— STRUCTURE OF THE FLOWER. 

When complete, the flower consists of four sets of organs, the 
outer set usually leaf-like and green, called the calyx, composed of 
individual pieces called sepals; the second set, usually delicate and 
brightly colored, called the corolla, made up of individual pieces 
called petals; the third set, called the andrcecium, made up of indi- 
vidual pieces called stamens; and the fourth, or central set, called 
the gynsecium, made up of individual pieces called pistils or 
carpels. Since the stamens and pistils are homologous with the 
spore-bearing leaves of the ferns, they are collectively called 
sporophylls. All of these parts grow from a shortened axis or 
stem called the receptacle. Fig. 169 is a diagram of a typical 
flower. The parts are represented as separated in their order from 
the receptacle: 

(a) Represents a set of three pistils, or carpels. 

(b) A set of three stamens. 



72 



PART I. — ORGANOGRAPHY. 



(c) A whorl of three petals, the corolla. 

(d) A whorl of three sepals, the calyx. 

(e) The receptacle, the shortened axis to which all these parts 
are attached; and 

(f) A bract below the flower. 





Fig. 170. 



Fig. 169. — Diagram of a typical 
ower ; a, the pistils ; b, the stamens ; 
c, the corolla,; d, the calyx; e, the re- 
ceptacle, and f, bract. 

Fig. 170. — Ground plan of the same 
flower, showing relation of parts. 



Fig. 169. 

Fig. 203 represents the ground plan of such a flower. The 
first, or outside cycle, represents the calyx, the second the corolla, 
the third the stamens, and the fourth, or central cycle, the carpels. 
It will be observed that the successive cycles alternate with each 
other. 

While the floral organs are usually arranged in whorls or 
cycles, corresponding to whorled leaves, yet the spiral arrange- 
ment corresponding to alternate leaves is not infrequent, occurring 
in all the sets, but more commonly in the inner ones, the sporo- 
phylls. By referring again to Fig. 169, it will also be seen that 



CHAPTER VIII. — THE STRUCTURE OF THE FLOWER. 73 

in this ground plan a certain number, the number three, prevails 
throughout. This is called the cycle number or numerical plan of 
the flower, an important thing to observe in the study of flowers, 
since in some large groups of plants the same number prevails 
throughout, as, for instance, the number three, or some multiple 
of it, in the great group of Monocotyledons, while in Dicotyledons 
five or, less commonly, four are the prevalent cycle numbers. A 
flower constructed on the plan of one, or which possess one sepal, 
one petal, etc., as is sometimes the case, is called monomer -ous; one 
whose parts are in twos, dimerous; one whose parts are in threes, 
trimerous-, one whose parts are in fours, tetramerous; one whose 
parts are in fives, pentamerous; and one whose parts are in sixes, 
hexamerous. The commonest of these arrangements are the tri- 
merous, the tetramerous, and the pentamerous. It must be 
observed that in some cases, owing either to the multiplication, 
suppression or coalescence of the parts of some whorls, the numer- 
ical plan is more or less obscured, but it may in most instances 
be discovered by careful study. 

Such a flower as is represented in Figs. 169 and 170, is tri- 
merous ; since, also, it possesses all the parts which properly belong 
to a flower, it is complete; because it has the same number of parts 
in each cycle, and these cycles alternate with each other regularly, 
it is symmetrical; because the parts of each set are similar in size 
and shape, it is regular; and because it possesses all the parts 
essential to the production of seed, namely, stamens and pistils, it 
is hermaphrodite, or perfect; and because it possesses both sets 
of the floral envelopes, calyx and corolla, it is dichlamydeous. 
Many typical angiospermous flowers possess two whorls of stamens. 
The flower of the Trillium, except that its three pistils are par- 
tially united, illustrates very well a typical trimerous flower, and 
the flowers of the Flax and the Stonecrop are pentamerous flowers 
that closely conform to the typical structure. But, while it is con- 
venient to compare flowers with some such form as we have 
described as typical, the flowers that differ from this form are far 
more numerous than those which conform to it. Most of these 
differences we regard as adaptations which the organs have under- 
gone in relation to the surroundings of the plant, or the conditions 
of its existence. The selection exercised by insects in visiting 
flowers for their nectar and pollen, in conjunction with the ten- 
dency which all flowers have to vary, has curiously enough been 



74 PART I. — ORGANOGRAPHY. 

proved to be one important agency in producing irregular and 
unsymmetrical flowers. (See the subject of Pollination.) 

The more important deviations from the typical form of the 
flower described in the foregoing paragraph may be classified as 
follows : 

(1) Suppression or Absence of Parts. A flower may be incom- 
plete in almost any degree. Only a portion of a single whorl may 
be absent, or one or more entire whorls may be wanting. There 
are flowers so reduced as to consist only of a single stamen, or of 
a single pistil, as in the little Wolffia, while others should be con- 
sidered rather as primitive and simpler forms. 

A flower that lacks one of the floral envelopes is called 
apetalous. Apetaly may result either from suppression of one set 
of floral leaves or from failure of the perianth to become differen- 
tiated into two sets or whorls. A flower that is destitute of both 
calyx and corolla is termed naked; if it has pistils, but is destitute 
of stamens, it is called pistillate, or female; if it possesses stamens, 
but not pistils, it is described as staminate, or male; and if it be 
destitute of both, it is called neutral. Such showy neutral flowers 
are seen in the border of the cymes of the wild Hydrangea and 
Cranberry-tree. 

Some plants, as the Begonias, Castor-oil Plant and Maize, bear 
two kinds of flowers, staminate and pistillate, on the same plant. 
Such a plant is described as monoecious. In the case of some others 
the staminate and pistillate flowers are borne by different indi- 
viduals of the same species; this is true of Sassafras, many Wil- 
lows, the Tree of Heaven, etc. Such plants are dioecious. The 
Maple is an example of a tree which produces staminate, pistillate 
and hermaphrodite flowers all on the same tree. Such a plant is 
termed polygamous. 

(2) Multiplication of Parts. This is scarcely less common, 
and may apply to any of the floral organs. So-called "double" 
flowers are flowers in which the petals or sepals are multiplied 
beyond the normal number, as in the cultivated Rose, the Camellia, 
and the garden Ranunculus. In the Cactuses, the stamens, and in 
the wild Buttercups, the pistils, are very numerous. Sometimes 
the multiplication of parts takes place by the formation of new 
whorls, and sometimes by an increase in the number of parts of 
the same whorl. 

(3) Anteposition of parts. Normally, as has been stated, the 
whorls alternate, but occasionally they are anteposed, or have the 



CHAPTER VIII. — THE STRUCTURE OF THE FLOWER 



75 



pieces of successive whorls placed one in front of the other. In 
the Barberry and the Blue Cohosh, for example, the stamens come 
opposite to the petals, and in the Iris the stigmas (which are the 
upper part of the pistil) come opposite the stamens. 

(4) Irregularity of Parts. Irregularity in the size, shape or 
coloring of parts, particularly of the calyx and corolla, is very 
common. Flowers which are radially symmetrical and therefore 
regular are termed Actinomorphic, while flowers which are irreg- 




Fig. 171. — Flower of Aconite; a, as it appears when fully expanded; c, with 
the parts separated, showing the hooded upper sepal, the two large lateral sepals 
and the two smaller ones; underneath the hood are the two petals. 



ular but may be divided in one plane so as to give similar halves, 
are said to be zygomorphic. In the Figwort and Mint families 
regularity is the exception and not the rule, and there is no known 
member of the family of Orchids that is not very irregular. Fig. 
171 represents the zygomorphic flower of Monk's-hood or Aconite. 
In the outer whorl there are five sepals, the upper of which is 
hooded, and the two lateral ones differ from the two lower in size 
and shape. From the second whorl, or corolla, all but two pieces 
are wanting, and these, though really petals, bear little resem- 
blance to ordinary ones in shape, a shows the flower as it appears 
naturally, and c represents the same with the parts of the calyx 
and corolla separated, showing their shape and relations. 

(5) Union of Parts. The growing together of parts may take 



76 



PART I. — ORGANOGRAPHY. 



place in two ways. Either the parts of the same whorl may be 
united partly or wholly, or parts of different whorls may have 
become more or less united. The former is termed coalescence, 
the latter actuation. Coalescence, either complete or partial, may 
occur between the members of any set of floral organs, and any 
two sets may become adnate partly or wholly. Even organs so 
different in their functions as stamens and pistils not infre- 
quently are united, as in the Orchid family. It is to be under- 
stood that such union of parts is congenital; it goes back to the 
development of these parts at the growing point of the floral stem. 
It would be a misconception to think of these coalesced parts as 
having been formed separately and then, later, united. 

Practical Exercises. 



Examine flowers of the following plants: The Tiger Lily, the House Gera- 
nium, the Morning-glory, the Butter-cup, and the Rose, and determine (1) the 
numerical plan of each flower, (2) draw a ground plan of each, representing, as 
in Figs. 162 and 170, the number and relation of parts, and note in each what 
deviations occur. 



CHAPTER IX.— THE TORUS, CALYX AND COROLLA. 

The Torus or Receptacle. This is the shortened axis from 
which the other floral organs grow. In form it is commonly convex 
or flat, but sometimes it is conical, as in the Strawberry, some- 
times long and beaked, as in the Geranium, sometimes concave or 
hollow, as in the Rose and Fig, sometimes top-shaped, as in 
Nelumbium. 




Fig. 172. 



Fig. 173. 



Fig. 174. 



Fig. 172. — Orange flower, cut lengthwise and deprived of its petals and all but 
one cluster of its stamens, to show the hypogynous disc, a. 

Fig. 173. — Flower of Sumach, cut lengthwise, showing perigynous disc, a. 
Fig. 174. — Flower of JEthusa, cut lengthwise to show the epigynous disc, a. 

Not infrequently the receptacle produces a fleshy outgrowth 
from its margin, called a disc. If this remains wholly under- 
neath the pistils, as in Fig. 172, it is said to be hypogynous; if it 



CHAPTER IX. — THE TORUS, CALYX AND COROLLA. 77 

grows up around and partially but not wholly envelops them, as 
in Fig. 173, it is called perigynous; and if it completely envelops 
them and become adnate to them, so as to appear to spring from 
the top of the ovary, as in Fig. 174, it is said to be epigynous. 

Since the torus is but a shortened axis, we may expect to find 
instances which show a lengthening of it. Such an elongation 
of the torus, when occurring between the calyx and corolla, is 
termed an anthophore; between corolla and the stamens a gono- 
phore, and between the stamens and the pistil a gynophore. In 
the Umbelliferse and some of the Geraniacex there is an upward 
prolongation of the torus which passes between the carpels and 
is attached to them. This is known as a carpophore. 

The axis of a flower cluster, if very short and resembling in 
shape the receptacle of a single flower, is also called a receptacle, 
or a common receptacle. The floral axes of the Dandelion, Let- 
tuce and Clover are examples. 

The Calyx and Corolla together constitute the Perianth or 
floral envelope. If these two whorls are similar in form and color 
the term Perigone is applied to them. 

The Calyx. This is the outer of the four series of floral leaves, 
and its parts ordinarily bear a closer resemblance to true leaves 
than do the other organs of the flower. They are more commonly 
green in color, and are then described as foliaceous, but in some 
flowers they have the color of petals or some lively hue other 
than green, in which case they are described as petaloid. The 
latter are illustrated in the sepals of the Larkspur, Columbine and 
showy Lady's-slipper. When the petals are distinct from each 
other or ununited, the calyx is described as chorisepalous, or, less 
correctly, as polysepalous, and when they are united either 
partially or wholly, it is called gamosepalous. In a gamosepalous 
calyx where the union of sepals is incomplete, the united portion 
is called the tube, while the free or ununited portion is termed 
the limb, and the orifice of the tube is called the throat. , 

In flowers belonging to the natural order Compositse, the calyx 
has its tube united to the ovary, while its limb is produced into a 
hairy, scaly or spiny crown called a pappus The down, by means 
of which the ripe fruits of the Dandelion, Thistle and Lettuce are 
wafted on the wind, is an illustration. In the Valerian and Teasel 
families, the calyx-limb forms a pappus in a similar manner. 

In form, the calyx may be regular or irregular: regular, if its 
parts are evenly developed; irregular, if some of the sepals are 



78 PART I. — ORGANOGRAPHY. 

larger or different in shape from others; or in the case of a gamo- 
sepalous calyx, if either the tube is unequal-sided or the divisions 
of the limb are of unequal size or shape. Among the more com- 
monly occurring forms of the gamosepalous calyx are the tubular 
or tube-shaped, the rotate or wheel-shaped, the campanulate or 
bell-shaped, the hypocrateriform or salver-shaped, the urceolate 
or urn-shaped, and the bi-labiate, forms which correspond to those 
of the corolla, presently to be described. 

The calyx very commonly remains after the corolla and stamens 
have withered, and sometimes endures even until the ripening of 
the fruit; in either case it is said to be persistent. Not infre- 
quently, however, it falls away at the same time with the corolla 
and stamens, when it is described as deciduous. More rarely it 
falls off when the flower begins to open ; in this case it is described 
as caducous; the Poppy and May-apple afford examples. 

The calyx often is more or less adherent to the ovary or base 
of the pistil, and it is a matter of importance in the study of 
flowers to observe whether such adhesion is present, and to what 
extent. When free from the ovary or situated wholly beneath 
it, the calyx is said to be inferior or hypogynous ; when its tube 
becomes adnate to and partially but not wholly envelops the ovary, 
the calyx is said to be half -superior or perigynous; and when the 
calyx completely envelops the ovary, so that the limb appears to 
arise from its very top, the calyx is said to be superior or epigy- 
nous. The terms mentioned above are firmly established in botan- 
ical nomenclature and are convenient descriptive expressions, yet 
convey a false impression, for in reality it is the end of the flower 
axis, the receptacle, that is directly involved. When the recep- 
tacle is conical, the ovary, being centermost, will of course be 
uppermost in the flower and is therefore "superior" while the 
calyx is "inferior" and the whole flower is "hypogynous." But in 
other instances the outer whorls spring from a cup shaped recep- 
tacle, the hypanthium, in the center of which the pistil is borne; 
the ovary is free from the hypanthium or but slightly attached to 
its base, implying a "perigynous" flower, or the hypanthium is 
grown fast to the ovary so that the floral parts appear to arise 
from the summit of the ovary, when the flower is "epigynous" and 
the ovary "inferior." See Figs. 194, 195 and 196. 

Sometimes we find exterior to the calyx or even adherent to it 
a whorl of bracts more or less resembling a calyx in appearance 
and structure. This is the case with the Hibiscus, the Strawberry 



CHAPTER IX. — THE TORUS, CALYX AND COROLLA. 



79 



and the Cinquefoil. Such an organ is called an epicalyx. See 
Fig. 177. 

In some cases bracts situated below the flower become more 
highly colored than the floral organs themselves, as in the Painted- 




Fig. 17; 



Fig. 176. 



Fig. 17/. 



Fig. 178. 



Fig. 179. 



Fig. 175. — Chorisepalous calyx of a species of Oxalis, somewhat enlarged. 

Fig. 176. — Gamosepalous calyx of a species of Abutilon. The inflated tube is 
five-winged. 

Fig. 177. — Campanulate calyx of a species of Hibiscus, a, one of the divi- 
sions of the limb ; b, the tube ; and c, one of the leaves of the epicalyx. 

Fig. 178. — Tubular calyx of Saponaria officinalis; a, the five-toothed limb; 
and b, the tube. 

Fig. 179. — Bi-labiate calyx of Salvia urticifolia, somewhat enlarged; a, three- 
toothed upper lip ; and b, two-toothed lower lip. 



cup and in some Euphorbias. These should not be confounded 
with the floral organs proper. 

The Corolla. This is usually the most showy portion of the 




Fig. 181. 



Fig. 182 



Fig. 183. 



Fig. 120. — Petal of Saponaria, one of the Pink family, a, blade ; b, 
corona ; c, claw. 

Fig. 181. — Flower of Genista, slightly enlarged, in front view. 

Fig. 182. — The same in lateral view. 

Fig. 183. — The petals of the same separated, x is the vexillum or standard; 
y, y', the alae or wrings; and z, z', the two petals which compose the carina or 
keel. 

flower. It is seldom green in color, but, like the sepals of the 
calyx, its parts often bear more or less resemblance in shape to 
leaves. In Fig. 180 is shown a petal of Saponaria. The upper or 



80 PART I. — ORGANOGRAPHY. 

expanded portion is termed the limb, blade or lamina. At the 
junction of the latter with the lower or stalk-like portion are 
observed two little projections, b. These constitute the corona. 
The stalk, c, is called the claw or unguis, and such a petal is said 
to be unguiculate or clawed. In the great majority of petals, 
however, the corona is wanting, and in many cases also the claw. 

The lamina is most commonly a flat expansion, resembling in 
this respect the majority of leaf-blades, but this is not always the 
case; it may be thread-like or filiform, club-shaped or clavate, 
spurred or calcarate, sac-shaped or saccate, etc. The flattened 
kinds present almost as great a variety of shapes as those of leaf- 
blades, and, like them, may have their margins entire or variously 
indented, incised, lobed, parted or fringed. The terms already 
learned in leaf-description are therefore also applicable, for the 
most part, in the description of petals. 

Where the petals are not at all united with each other, the 
corolla is described as choripetalous, or, less correctly, as polypet- 
alous. If the distinct petals are four in number and arranged 
in the form of a cross, as they are in the Cress family, it is called 
cruciform; if the petals are five and short-clawed or clawless and 
spreading, like those of the wild Rose, it is called rosaceous; if 
there are five long-clawed petals, having the claws concealed in the 
tube of a gamosepalous calyx, as in the Pink, it is called caryophyl- 
laceous, Fig. 248; when it is shaped like the irregular flower of 
the Pea or Genista, it is called papilionaceous, Figs. 181, 182 and 
183; when calyx and corolla each consist of three pieces closely 
resembling each other in form and color, as in the Lily and Tulip, 
the flower is called liliaceous; and when, as in the Orchidacese, 
the floral leaves are epigynous, and calyx and corolla are in whorls 
of three pieces each, and one of the petals, called the lip, has a 
shape markedly different from the rest, it is called orchidaceous. 
In flowers like the latter two, where calyx and corolla closely re- 
semble each other, they are commonly not distinguished by sep- 
arate names, but the two together are called the perianth. 

But the petals very often become more or less united. In this 
case the corolla is described as gamopetalous or sympetalous. The 
united portion is called the tube, and the free portion, the limb, 
as in the calyx. 

A gamopetalous corolla is called rotate, or wheel-shaped, when 
the tubular portion is short, and the divisions of the limb radiate 
from it like the spokes of a wheel, as in the corolla of the Potato, 



CHAPTER IX. — THE TORUS, CALYX AND COROLLA. 



81 



Fig. 184; campanulate, or bell-shaped, when shaped like the Hare- 
bell, Fig. 185; urceolate, when oblong or globular, with the mouth 
somewhat contracted, as in the flower of the Wintergreen, Fig. 
186; infundibular, or funnel-shaped, when it flares like a funnel, 




Fig. 184. 



Fig. 185. 



Fig. 186. 



Fig. 187. 



Fig. 184. — Flower of Potato, illustrating rotate corolla. 

Fig. 185.— Flower of Harebell, illustrating campanulate corolla. 

Fig. 186. — Flower of Wintergreen, illustrating urceolate corolla. 

Fig. 187. — Flower of Morning-glory, illustrating infundibular corolla. 

as in the Morning-glory, Fig. 187; hypocrateriform, or salver- 
shaped, when the slender, tubular portion is crowned by a limb 
expanded at right angles to it, as in Phlox, Fig. 188; tubular, when 
the limb is small or scarcely spreading, and the tube is elongated, 
as in the flower of Spigelia, Fig. 189; ligulate, when, as in Fig. 




Fig. 188. 



Fig. 189. Fig. 190. 



Fig. 191. 



Fig. 192. 



Fig. 188. — Flower of Phlox, illustrating hypocrateriform corolla. 

Fig. 189. — Flower of Spigelia, illustrating tubular corolla. 

Fig. 190. — Flower of Chrysanthemum, one of the Compositae, illustrating a 
ligulate corolla. 

Fig. 191. — Bi-labiate flower of Sage. The corolla is also ringent. 

Fig. 192. — Personate corolla of Linaria vulgaris. The corolla is also calcarate 
at the base. The thickening, a, is called the palate. 

190, the lower portion is tubular, but the upper flattened and 
strap-shaped; labiate, when, as in the flower of the Deadnettle 
and Sage, Fig. 191, there are two lips; it is also ringent, if the 



82 



PART I. — ORGANOGRAPHY. 



lips spread wide apart, as in the last figure; and if they are 
closed, and have thickened lips, as in Snap-dragon and Linaria, it 
is personate. A gamopetalous corolla may also be saccate or 
calcarate, the same as one whose petals are distinct. The corolla 
of Linaria, Fig. 192, is both personate and calcarate. 

The margins of gamophyllous calyxes and corollas may be 
variously indented or lobed, the same as those of leaves, and the 
same terms are used in describing them. 

Practical Exercises. 

Study the torus, calyx and corolla of the following flowers, observing care- 
fully their structure and describing them fully, using the proper descriptive 
language of botany: Those of the Petunia, Strawberry, Wild Lupine, Water- 
lily, Dandelion, Lady's-slipper, Lobelia, Rose, Paeony, and Wallflower. State also, 
from your examination of them, which of these flowers have a disk, what its 
shape is in each case, and whether it is hypogynous, perigynous or epigynous. 



CHAPTER X.— THE STAMENS, OR ANDRCECIUM. 

The Andrcecium is composed of sporophylls which are modified 
for the production of microspores or pollen grains and are there- 
fore termed microsporophylls or, more commonly, stamens. 

The stamens are the male organs of reproduction, and each 
stamen, when complete, consists of a filament, or stalk, which is 




Fig. 194. Fig. 195. Fig. 196. 

Fig. 193. — A stamen, consisting of a pollen-bearing part, the anther, a, and a 
stalk or filament, b. 

Fig. 194. — Diagram of flower showing hypogynous calyx, corolla and stamens. 

Fig. 195. — Diagram of flower showing perigynous corolla and stamens. 

Fig. 196. — Diagram of flower showing epigynous calyx, corolla and stamens. 
In each of these three figures, a represents the calyx ; b, the corolla ; c, a stamen ; 
and d, the pistil. 

not essential, and an anther, the essential portion, which contains 
in its interior a fine powder, the microspores or pollen. See 
Fig. 193. 



CHAPTER X. — THE STAMENS. 



83 



Stamens are said to be definite in number when so few as to be 
readily counted, as in the flowers of the Barberry, Mustard and 
Geranium, and indefinite when very numerous, making it difficult 
to count them, as in the Buttercup, the Rose, and the Water-lily. 

As to their attachment, they may be situated on the receptacle, 
as in the Poppy, when they are said to be hypogynous; or they 




Fig. 199. 



Fig. 200. 



Fig. 197. Fig. 198. 

Fig. 197. — Gynandrous stamens of the Lady's-slipper, one of the Orchidaceae ; 
s, represents the stigma, and a, a', the anthers; they are grown together. 

Fig. 198. — Monadelphous stamens of the Mallow; s, the stigmas, and a, the 
anthers. 

Fig. 199. — Diadelphous stamens of the Pea. In this flower, one stamen 
stands by itself, while the other nine are united by their filaments. 

Fig. 200. — Polyadelphous stamens of the Orange. 

Fig. 201. — Syngenesious stamens of the Dandelion; a, the anthers; and st, 
the stigma. 

may be borne on the margin of the calyx- tube or of the hypan- 
thium, as in the Apple and Cherry, when they are said to be 
perigynous; or they may arise from the top of tiie ovary, as in 
the Fennel and Madder, when they are called epigynous. See 
Figs. 194, 195 and 196. In the majority of cases where the corolla 
is gamopetalous, the stamens are inserted on its tube, as in the 
Phlox; they are then described as epipetalous. Sometimes they 
grow fast to the pistils, as in the Orchidacex, Fig. 197, when they 
are called gynandrous. 

Very commonly, stamens may be more or less united with each 
other. This union may take place by the filaments, or by the 
anthers, or by both. By their filaments they may be grown 
together into one or into more than one set. When in one set, as 
in the Mallow, Fig. 198, they are called monadelphous; when in 
two sets, as in the Pea, Fig. 199, they are termed diadelphous; 
when in three sets, as in some Hypericums, triadelphous, etc. ; and 
when in a considerable number of sets, as in the Orange, Fig. 200, 
they are called polyadelphous. When stamens are united by their 
anthers, as they are in the Sunflower, Dandelion (Fig. 201), and 
other Composite, they are called syngenesious. 



84 



PART I. — ORGANOGRAPHY. 



In some flowers, as in many Mints and Figworts, there are 
four stamens, two of them longer than the other two; such sta- 
mens are said to be didynamous. In the Mustard and other mem- 
bers of the Cress family, there are four long and two short ones; 
the stamens of such flowers are said to be tetradynamous. 

Occasionally the filament is wanting, and the anther is then 
described as sessile. Sometimes, however, the anther is wanting, 
or no longer functional; such sterile or abortive stamens are 
termed staminodia. 

The Filament. This is the stalk of the anther. It assumes a 
great variety of forms in different flowers. Sometimes it is 
capillary, or very slender and hair-like, as in some grasses; some- 
times it is filiform, or thread-like, as in many of the Rosacese; 
sometimes it is petaloid, or petal-like, as in some of the stamens of 
the White Water-lily; sometimes it is toothed, as in some species 
of Onion; sometimes it is appendaged, as in the Milk- weed; most 
commonly it is simple, as in the Geranium, but sometimes it is 
branched, as in the Castor-oil Plant. Its different forms commonly 
bear some relation, more or less evident, to the mode of pollination. 

The Anther. The anther is usually two-lobed and two-celled, 
that is, contains two pollen-sacs or thecse, but occasionally we 
find it twice as many lobed and celled, and, on the other hand, 




202. 203 



Fig. 202. — Stamen of Saxifrage, showing innate anther. 

Fig. 203. — Stamen of Magnolia, showing adnate anther. 

Fig. 204. — Stamen of Agave, showing versatile anther. 

Fig. 205. — Stamen of Alchemilla, showing anther dehiscing transversely. 

Fig. 206. — Stamen of Barberry, showing anther dehiscing by valves. 

Fig. 207. — Stamen of Rhododendron, with anther dehiscing by pores or open- 
ings at the apex. 

Fig. 208. — Stamen of Asarum, with connective prolonged beyond the top of 
the anther. 

Fier. 209. — Upper portion of stamen of Oleander, with connective prolonged 
and forming a plumose appendage at the top of the anther. 

Fig. 210. — Stamen of Butomus, showing four-celled anther. 



CHAPTER X. — THE STAMENS. 



85 



we sometimes find stamens where, as in those of the Hollyhock, 
the two normal pollen-sacs have become confluent into one. 

There are different ways in which the anther may be attached 
to its filament. When it stands erect on the end of the filament, 
as in Fig. 202, it is described as innate; when the two lobes of the 
anther appear to grow fast to the side of the filament, or the latter 
appears to be produced through the middle of the anther, as in 
Fig. 203, it is called adnate; and when the anther swings freely 
on the slender apex of the filament, as in Fig. 204, it is called 
versatile. 

It is of importance, also, to observe which way the anther 
faces in the flower, whether inward toward the pistil, or outward 
from it, or whether its position is indifferent. Most versatile 
anthers are indifferent, and other kinds also are frequently so, 







Fig. 211. 



Fig. 212. 



Fig. 213. 



Fig. 214. 



Fig. 211. — Stamen of Calaminth, showing anther with broad connective, a. 

Fig. 212. — Stamen of Sage, with elongated connective hinged to the top of 
the filament. One lobe of the anther, a, contains pollen, the other, b, is sterile. 

Fig. 213. — Stamen of Hollyhock, with anther lobes confluent. 

Fig. 214. — Stamen of Globe Amaranth, with anther consisting of but one 
lobe, and that attached by its middle to the end of the filament. 



especially when the filaments are long and slender. Anthers 
which face outward are described as extrorse, while those which 
face inward are introrse. 

Anthers split open or dehisce, in a variety of ways, to shed 
their pollen. When the dehiscence is lengthwise of the anther, 
as in Figs. 202 to 204, inclusive, it is said to be longitudinal; when 
crosswise, as is shown in Fig. 205, it is descirbed as transverse; 
when it opens laterally by lids, as in the Barberry, Fig. 206, it is 
called valvular; and when tjie discharge of the pollen is by pores 



86 PART I. — ORGANOGRAPHY. 

at the apex, as in most members of the Heath family, Fig. 207, the 
dehiscence is called porous. 

The Connective. The connective is that part of the anther 
which unites the two lobes, or what appears to be the continuation 
of the filament through the anther. In some anthers, as for 
example those of Wild Ginger (Asarum) , Fig. 208, and the Olean- 
der, Fig. 209, it is prolonged beyond the top of the anther; in 
others, as in Calaminth and Sage, Figs. 211 and 212, it is broad, 
or strongly developed transversely, and separates rather widely 
the two lobes; in the latter the lobes are very wide apart, and one 
of them becomes abortive, while the other remains fertile; in 
others still, as the Hollyhock, the connective disappears and the 
two equal lobes become confluent into one, Fig. 213, and in the 
Globe Amaranth of the gardens one of the cells entirely dis- 
appears, as well as the connective, while the other is attached by 
its middle to the end of the filament, as in Fig. 214. Such an 
anther, as the last, has been termed dimidiate. 

The Pollen. This appears to the unaided eye as fine, dust-like 
particles, produced by the mother cells within loculi of the anthers. 
It is for the production of pollen that the stamens exist, and when 
it is shed their work is done, and they usually wither away. Each 
pollen grain is commonly a single cell with two walls, the outer, 
called the extine, thickened and often peculiarly marked, the 
inner, called the intine, thin, highly extensible, and inclosing a 
semi-fluid substance called the fovilla. 

Some idea of the variety of forms of these grains may be 
gained from an inspection of Figures 215 to 221 inclusive. 

When a pollen grain is placed upon the stigma of a flower of 
the same species, the outer coat of the grain bursts, and by the 
extension of the inner one, a tube is formed which penetrates the 
tissues of the style. Fig. 220 represents a germinating pollen 
grain. 

Pollen grains are produced in enormous numbers, particularly 
in plants that are dependent on the wind for the transfer of the 
pollen from the stamens to the pistils, as in the Pines. It has 
been estimated that a single plant of the Chinese Wistaria, when 
well developed, may produce during one flowering season as many 
as 27,000,000 pollen grains. A common Pine tree, in all probabil- 
ity, produces a vastly greater number than this. 

It is to be observed that in plants that are dependent on the 
wind for the transfer of their pollen, the grains are usually dry 



CHAPTER X. — THE STAMENS. 



87 



and powdery; while those that depend on insects for this work, 
usually produce sticky pollen. In some instances, however, the 
pollen does not separate into grains, but remains in masses, as in 





Fig. 221.— Pollinia of the 
Milk-weed. 
Fig. 218. Fig. 219. Fig. 220. 

Fig. 215. — Spinose pollen grain of the Mallow. V 

Fig. 216. — Pollen grain of Lily. 
Fig. 217. — Pollen grain of Chicory. 
Fig. 218. — Pollen grain of Evening Primrose. 
Fig. 219. — Pollen grain of Pine. 
Fig. 220. — Pollen grain in process of germination. 



\ All highly magnified. 



the flowers of the common Milk-weed and those of most Orchida- 
cex. These pollen masses are termed pollinia. The pollinia of 
the Milk-weed are illustrated in Fig. 221. 

Practical Exercises. 

Examine the stamens of the freshly opened flowers of the following plants : 
The Pumpkin, the common Mallow, the Tiger Lily, the Cherry, the Musk Plant, 
and the Wild Cucumber, and ascertain in each case (1) what parts are present; 
(2) whether the stamens are distinct or whether they are united to each other 
or to other organs; (3) whether they are hypogynous, perigynous, or epigynous ; 
(4) whether the position of the anthers is extrorse, introrse or indifferent; (5) 
whether the anthers are one-celled, two-celled or four-celled; (6) the character 
of the connective; (7) whether the anthers are innate, adnate or versatile; (8) 
whether their dehiscence is longitudinal, transverse, valvular or porous; (9) the 
shape and character of the filaments; (10) the shape and markings of the pollen 
grains. In order to study the pollen grains, seize by means of a delicate pair of 
forceps, a stamen whose anther is just dehiscing, tap the latter gently on the 
surface of a clean sheet of white paper, and then examine carefully the adhering 
grains by means of a good lens. The pollen grains of many plants are so minute 
that they cannot be satisfactorily studied in this way ; the student had better, 
therefore, use a microscope for the purpose. 



88 



PART I. — ORGANOGRAPHY. 



CHAPTER XL— THE PISTILS, OR GYN^ECIUM. 

The pistil is the female organ of reproduction of the flowering 
plant. It is composed of one or more sporophylls known as 
carpels. In the Pine and related plants, it consists of an open 
leaf or scale, which bears but does not inclose the ovules (see Fig. 
222) ; but in most flowering plants it forms a closed sac which 
envelops and protects them. Pistils of the former kind are called 
gymnospermous ; they are usually quite simple in their structure 
(Fig. 222) ; those of the latter kind are termed angiospermous, 
and they exist in a great variety of forms. When complete, an 
angiospermous pistil consists of ovary, style and stigma. 





Fig. 223. Fig. 224. 

Fig. 222. — Scale from a young cone of Pine, bearing two ovules. 

Fig. 223. — A leaf folded so as to illustrate the structure of a simple pistil or 
carpellary leaf. 

Fig. 224. — A simple pistil cut transversely to show the cavity of the ovary 
and the ovules, a is the stigma and b the style. 



The ovary, usually the basal portion, is the part which con- 
tains the ovule or ovules; the stigma, commonly the apical portion, 
is the part which receives the pollen, and the style the part which 
connects the ovary and stigma, Fig. 224. The former two are 
essential, while the latter is not. When the style is wanting, as is 
frequently the case, the stigma is said to be sessile. 

The pistil is regarded as having been developed from the sporo- 
phyll of flowerless ancestral forms rather than as being closely 
related to foliage leaves. But sporophylls are leaves modified for 
reproductive functions and, in this sense, pistils are homologous 
with leaves. If we imagine an ordinary leaf, like that of the 



CHAPTER XI. — THE PISTILS. 



89 



Cherry, to be folded in such a manner as to bring the upper 
surface and margins interior, as in Fig. 223, the lower portion 
would correspond to the ovary, the infolded margins projecting 
into its cavity to the ovule-bearing portion, or placenta, the apical 
portion to the stigma, and the narrow upper portion of the leaf 
adjacent to it, to the style. If the ripe follicle of the Columbine 
or of the Caltha be opened out, as in Fig. 225, the correspondence 
in structure to the infolded leaf above described, will be at once 
evident. 

If a Pea-pod be carefully laid open and examined, the young 
peas will be found to occupy a double row along one of the sutures 
of the pod, as illustrated in Fig. 226. This portion corresponds 
to the infolded edges of the leaf, and when the pod splits open it 




Fig. 225. 



Fig. 226. 



Fig. 225. — Follicle of Caltha, opened out to show its resemblance to a leaf. 
Fig. 226. — Pea-pod, laid open to show the placenta, corresponding to the 
infolded leaf margins, and bearing a double row of ovules. 



does so along the line separating these edges. This line is called 
the ventral suture. But in also dehisces along the opposite side, 
called the dorsal suture, and this corresponds to the mid-rib of the 
leaf. The pistils of the Caltha, the Columbine and the Pea are 
each made up of a single carpel. Such pistils are described as 
apocarpous or simple. Other examples of apocarpous pistils are 
those of the Buttercup, Blackberry, Golden-seal and Aconite. But 
pistils, more than any other floral organs, are liable to cohere 
more or less completely into compound forms. Such pistils are 
described as syncarpous, or compound, Figs. 227 and 228. 

The union may have all degrees of completeness. Sometimes, 



90 



PART I. — ORGANOGRAPHY. 



as in Saxifrage, Fig. 229, the ovaries are united below, but distinct 
above; often they are completely united, while the styles and stig- 
mas are distinct, as in the Flax and Hypericum, Figs. 231 and 
228; sometimes the union is complete, even to stigmas. Even in 
these cases, however, traces of the composite character of the 
structure usually still remain, either in the lobing of the stigma 
or ovary, or in the internal structure of the latter organ. If, for 
instance, the pistil is three-carpelled, the fact may be indicated 
by the division of the ovary into three cells, or by the fact" of its 




Fig. 227. 



Fig. 228. 



Fig. 227. — Syncarpous pistil of Scrophularia, made up of two carpels, 
ovary is cut transversely, to show the two- celled ovary. 

Fig. 228. — Syncarpous pistil of a species of Hypericum, composed of three 
carpels. 

Fig. 229. — Pistil of Saxifrage, having the two carpels only partialy united. 

Fig. 230. — Two-carpelled pistil of Henbane, with the ovary cut transversely 
to show the placentae. 

Fig. 231. — Pistil of Flax, consisting of five carpels, the ovaries united, but the 
styles and stigmas distinct. 



possessing three double rows of ovules on its walls. While, how- 
ever, the number of cells in the ovary is usually indicative of the 
number of carpels of which the pistil is composed, it must not be 
taken as an infallible guide, but other structural points must be 
taken into consideration, for instances are known where, by the 
growth of false partitions from the dorsal sutures of the carpels, 
the number of cells in the ovary has become double the number 
of carpels. Similarly, though the number of lobes of the stigma 
usually indicate the number of carpels, this is not always the case. 
Placentation. According to the character of the placentation, 
syncarpous pistils may be divided into four kinds: 

(1) Those with parietal placentae. In this case the ovary has 



CHAPTER XI. — THE PISTILS. 91 

but one cell or loculus, and the ovules are borne on the infolded 
edges of the component carpels, as shown in Fig. 232. Here, the 
number of double rows of ovules corresponds with the number of 
carpels which compose the pistil. Many apocarpous pistils, as 
those of the Pea and Caltha, also have this kind of placentation. 
(2) Those with axile placentae. In this case, the ovule bear- 
ing margins of the carpel grow inward until they meet in the 
center forming an ovary which usually has as many loculi as there 
are carpels composing it, as in Fig. 233. Thus the ovary with 
axile placentae is a modification of one with marginal placentae, 
and, as might be expected, we find every gradation between the 






Fig. 232. . Fig. 233. Fig. 234. 

Fig. 232. — Diagram of ovary, with marginal placentae. 

Fig. 233. — Diagram of ovary, with axile placentae. 

Fig. 234. — Diagram of ovary, with marginal placentae, but with the latter 
extended toward the centre of the ovary, constituting a form intermediate between 
those represented in Figs. 232 and 233. 

two. Fig. 234 represents an intermediate form, in which the mar- 
ginal placentae are prolonged inward, but do not meet. 

(3) Those with free-central placentae. Here, the ovules are 
borne on a column which rises free from the bottom of the ovary, 
as in the Primrose and the Soapwort. This form of placentation 
is illustrated in Figs. 235 and 236. 

The Style. This is the stalk of the stigma, or the part of the 
pistil which connects the stigma with the ovary. It sometimes 
contains a narrow canal or passage-way leading from the one to 
the other, but more commonly this is wanting, and the interior 
is composed of thin-walled cellular tissues. It most commonly 
arises from the summit of the ovary, in which case it is described 
as terminal or apical; in some cases, however, it is inserted on 
one side, as in the Strawberry, when it is called lateral, or it may 
even be attached to the base of the ovary, as in Alchemilla, when 
it is described as basilar. Very commonly the style falls away 
after the process of fertilization is completed, in which case it is 
termed deciduous, but sometimes it remains and forms a part of 



92 



PART I. — ORGANOGRAPHY. 



the fruit; it is then called persistent. This is the case in Snap- 
dragon and Scrophularia. As regards its form, it may be filiform 
or thread-like, as in the Fuchsia; clavate or club-shaped, as in the 
Orange; subulate or awl-shaped, is in Cyclamen; petaloid or petal- 
like, as in Iris. It may also be either simple or branching. In the 
case of syncarpous pistils, the styles may be united to any degree, 
from a slight union at the base to one which is complete to the 
apex. In these cases the terms used in the description of leaf- 
margins may be applied to them to indicate the degree of separa- 
tion, as trifidj quadrifid, tripartite, quadripartite, trilobate, quadri- 
lobate, etc. So far as the surface is concerned, it may be smooth 
or it may be hairy, and the hairs may be of various kinds. In the 
Composite the upper part is covered with rigid, collecting hairs, 
serviceable in brushing out the pollen from the anthers, and in 
some members of the Leguminosx a ring or fringe of stiff hairs, 
just beneath the stigma, prevents the pollen from falling upon the 
stigma of the same flower. 

The Stigma. This is the part which receives the pollen. It is 
either destitute of an epidermis or covered with a very thin one, 
secretes a viscid secretion, and is usually more or less roughened 





Fig. 235. Fig. 236. 

Fig. 235. — Pistil of Primrose, with 
ovary cut vertically to show free- 
central placentation. Enlarged. 

Fig. 236. — Pistil of Pinguicula, 
enlarged and cut transversely to 
show free-central placentation. 




/ 3 



Fig. 237. — Diagram 
of an ovule in longi- 
tudinal section, show- 
ing its various parts ; 
a, micropyle ; b, pri- 
mine ; c, secundine ; d, 
nucellus ; e, chalaza ; 
and f, funiculus. 



or papillose. This structure doubtless has reference to securing 
the pollen that is conveyed to it and ensuring its germination. In 
form and character the stigma differs much in different flowers. 
It may be terminal, or located at the apex of the style, or it may 



CHAPTER XI. — THE PISTILS. 93 

be lateral or confluent down its side; it may be simple or lobed; 
it may be discoid or flattened and disk-like, hemispherical, globular, 
filiform, petaloid, plumous or feathery, radiate or rayed like the 
cpokes of a wheel, stellate or star-shaped, cucullate or hooded, 
flabellate or fan-shaped, rostrate or beaked. 

The Ovule. The ovules are the small bodies in the ovary, which, 
after fertilization, develop into seeds. They are usually borne on 
a definite ovule-bearing portion of the interior of the ovary, called 
the placenta, but occasionally they occur without order on any 
portion of the ovary walls. 

A complete ovule, Fig. 237, consists of a nucellus, or body, two 
coats, the outer called the primine and the inner the secundine, 
and a funiculus or stalk. The coats do not completely enclose the 
nucellus, but a little opening for the reception of the pollen tube 




Fig. 238. 



Fig. 239. 



Fig. 240. 



Fig. 241. 



Fig. 238. — An atropous or orthotropous ovule. 

Fig. 239. — A campylotropous ovule. 

Fig. 240. — An amphitropous ovule ; a, raphe ; b, hilum. 

Fig. 241. — An anatropous ovule; a, chalaza ; b, micropyle ; anl c, raphe. 



is left at the apex. This opening is called the micropyle or fora- 
men. The base of the ovule, where the coats are attached to each 
other and to the nucellus, is called the chalaza. The point of at- 
tachment of the funiculus to the rest of the ovule is called the 
hilum. In some ovules the funiculus grows fast to the ovule for 
a portion of its length, as in Figs. 240 and 241. The adherent 
portion is called the raphe. 

It is frequently the case that some parts of the ovule are want- 
ing. The funiculus is often absent, and the ovule is then said to 
be sessile; in gymnospermous plants, like the Pine and Fir, only 
one of the coats is usually present; and in the Mistletoe and its 
allies, both coats are wanting. 

It is sometimes of importance to observe the position of the 
ovule in the ovary. It is erect, when it rises upright from the 



94 PART I. — ORGANOGRAPHY. 

bottom of the cavity of the ovary; it is ascending, when it rises 
obliquely from near the bottom; it is horizontal, when borne on 
the side of the ovary wall and pointing in a transverse direction; 
it is pendulous, when directed obliquely downward from near the 
top of the cavity, and it is suspended, when hanging from the very 
top of the cavity. 

The shape of the ovule itself is also to be regarded. An atro- 
pous. or orthotropous ovule is one that is straight, and has the 
hilum and micropyle at opposite ends, as in Fig. 238; a campylo- 
tropous ovule is one whose body is bent so that the hilum and 
micropyle are approximated, as in Fig. 239; an amphitropous 
ovule is one that is partly inverted; that is, one that has the funic- 
ulus located near the middle of the straight body of the ovule and 
pointing in a direction at right angles to it, as in Fig. 240; and 
an anatropous, or inverted ovule, is one whose chalaza is at one 
end, and hilum and micropyle adjacent to each other at the oppo- 
site end, as in Fig. 241. In the latter two kinds, the funiculus is 
adherent to the body of the ovule for a portion of its length; it is 
this adherent portion that is called the raphe. Inverted, or partly 
inverted, ovules are much more common than straight or bent ones. 

Practical Exercises. 

Study the flowers of the following plants with reference to the pistils : The 
Poppy, the Stramonium, the Lily, the Pumpkin, the Rose, the Hollyhock, and 
the Indian Corn. Determine (1), the parts of the pistil present in each case; 
(2) whether the pistils are apocarpous or syncarpous, and if the latter, state the 
degree of union; (3) the placentation of the ovary — that is, whether it is parie- 
tal, axile or free-central; (4) to what degree, if at all, the ovary is adherent to 
adjacent organs; (5) the position and shape of the style; (6) the position and 
shape of the stigma; (7) the arrangement of the ovules in the ovary; and (8) 
the shapes of the ovules. 

In studying the ovules and placentation, the student should make careful 
longitudinal and transverse sections of the ovaries with a very sharp knife ; 
they may then usually be studied satisfactorily by means of a good lens, but in 
some cases, where the ovules are quite small, the microscope will be indispensable. 



CHAPTER XII.— POLLINATION AND FERTILIZATION. 

Pollination. This consists in the conveyance of the pollen from 
the stamen to the pistil in such a manner as to produce fertiliza- 
tion, or cause the settling of seed. At one time it was supposed 
that most flowers possessing both stamens and pistils were self- 
fertilizing — that Nature's design in placing the two organs so 
near together was to make sure of bringing the pollen in contact 
with the stigma of the same flower. There are, indeed, some 



CHAPTER XII. — POLLINATION AND FERTILIZATION. 95 

instances in which this is the case, and such flowers, since they 
are habitually self-fertilizing, are called autogamous. But flowers 
of this kind are now known to be comparatively rare, and cross- 
fertilization, or allogamy, that is, the fertilization of the ovules by 
pollen derived from another flower, is the general rule. Most 
flowers are so constructed that external agencies of various kinds 
are utilized for this purpose, and the appliances by means of 
which the result is secured and close-fertilization prevented, are 
sometimes very elaborate and wonderful. Even where the anther 
and the stigma are in the closest juxtaposition in the same flower, 
the pollen, in many cases, is effectually prevented from reaching 
the stigma, while the arrangements at the same time are such as 
to insure its being brought to it from another flower. It is evident 
from the pains Nature has taken to secure the result, that some 
great advantage must accrue to the plant or its offspring from 
cross-fertilization, and this has also been proved to be the fact 
by careful and extended experiments. It is proved that there are 
some plants that utterly refuse to set seed when supplied with 
only their. own pollen, that there are others which greatly prefer 
pollen from another plant, and refuse to utilize their own when 
that from another of the same species is placed upon the stigma, 
and it is proved that in the great majority even of those plants 
which are capable of self-feritilization, stronger, hardier and more 
numerous offspring result from cross-fertilization. 

The external agencies utilized by the plant to bring about 
cross-fertilization are chiefly the wind and insects. Humming- 
birds, and some other species of birds that habitually visit flowers, 
are occasionally of service, and in the case of some aquatic plants 
currents are made use of; but these agencies are comparatively 
unimportant. 

Flowers whose pollination is effected by means of the wind are 
called anemophilous. Such flowers differ markedly in appearance 
and structure from those in which insects are the agents. They 
are usually provided with stigmas that expose a good deal of 
surface to the wind; they produce great abundance of dry, pow- 
dery pollen; they are without showy floral envelopes; they are 
without nectar, and they are destitute of perfume. Frequently, 
also, but not always, the pistils and stamens are in separate 
flowers, thus making self-fertilization impossible. 

The difference between the extent of surface exposed by the 
stigmas of anemophilous flowers and those pollinated by insect 



96 



PART I. — ORGANOGRAPHY. 



agency will be seen by reference to Figs. 242 . to 247, inclusive. 
The three figures at the left represent, respectively, the pistils of 
Wheat, Rush and Hemp, all anemophilous, and the three at the 
right, the pistils of the Tobacco, Foxglove and Centradenia flori- 
bunda, all of which are pollinated by insect agency. The enormous 
quantities of fine pollen produced by such anemophilous plants as 
the Pines and Indian Corn, and the great distances to which it is 
wafted, are facts familiar to every observing mind. The Oaks, 
Poplars, Birches, Walnuts, Grasses, Sedges, Plantains, Nettle and 
Hop are examples of wind-pollinated plants. 




Fig. 242. 




Fig. 244. 



Fig. 245. Fig. 246. Fig. 247. 

Fig. 242.— Pistil of Wheat, showing a pair of long feathery"] 
stigmas. § All 

Fig. 243. — Pistil of a Rush, showing three elongated, hairy I ane moph- 
stigmas. j n ous . 

Fig. 244. — Pistil of Hemp, with two slender and much elongated, i 
hairy or papillose stigmas. J 

Fig. 245. — Pistil of Tobacco, with small, somewhat two-lobed,] 
capitate stigma. , 

Fig. 246.— Pistil of Digitalis, showing small, two-lobed stigma. entomopn- 

Fig. 247. — Pistil of Centradenia floribunda (enlarged), showing nous, 

small papillose stigma. I 



Flowers which are cross-fertilized by the agency of insects are 
called entomophilous. They include all those with showy calyx, 
corolla or bracts, all perfumed flowers, all nectar-bearing, and all 
irregular flowers. The gay colors and perfumes are to attract 
the attention of insects, the nectar to reward them for their serv- 
ices, and the irregularities are adaptations of the flower to their 
visits, the character of the adaptation being such as to render 
cross-fertilization by their aid more certain. Bright colors and 
perfume sometimes go together, and the flower offers a double 
attraction to the insect visitor; but more commonly highly colored 
flowers are not odorous, or are but faintly so, and conversely, 



CHAPTER XII. — POLLINATION AND FERTILIZATION. 97 

highly odorous flowers are commonly not showy. Flowers with 
corollas of some shade of red or blue are usually visited by diurnal 
insects, while those with white or light-yellow corollas are often 
visited by moths and other insects that fly at dusk, these colors 
being more readily perceived in the dim light than others. It is 
by no means true, however, that all white flowers are fertilized 
by crepuscular insects. 

Even the stripes or lines found on corollas are significant; 
they point to the locality in the flower where the nectar is se- 
creted, and serve the purpose of guiding the insect thither. 

The disagreeably odorous flowers are attractive to some insects 
no less than the pleasantly odorous ones are to others. The giant 
flower of Rafflesia, for instance, has a carrion-like odor and a 
beefy appearance which attract swarms of carrion-flies that are 
deceived into depositing their eggs upon it, dooming their maggot 
progeny to starvation; in the process, however, they are likely to 
bring pollen from another flower and deposit it on the stigma. 
Some flowers which are visited by night-flying insects withhold 
their perfumes by day, but dispense them freely at night, as in 
the case of the night-blooming Oestrum nocturnum. Some flowers, 
also, that are cross-fertilized by day-flying insects, close at night, 
doubtless, in some instances at least, to prevent the wastage of 
nectar and pollen by insects that could not be of service to the 
plant. 

We may briefly summarize, as follows, the different means by 
which self-fertilization is prevented among entomophilous plants. 

(1) By the separation of the flowers into staminate and pistil- 
late forms, that is by diclinism. Diclinous plants are of two kinds : 
monoecious, as the Begonia, where both kinds of flowers occur on 
the same plant, and dioecious, as most Willows, where the male 
and female flowers occur on different plants. 

(2) By dichogamy, or the maturing of the male and female 
organs at different periods. This, occurring in flowers which 
possess both stamens and -pistils, is the same in its effects as 
though the male and female organs were in separate flowers. 
There are two kinds of dichogamy, one in which the stamens first 
mature and then afterward the pistils, and the other in which this 
order is reversed and the pistils are the first to mature. Flowers 
of the former kind are called proterandrous, while those of the 
latter are called proterogynous. Examples of proterandry are 
afforded by the Pinks, Gentians, many of the Composite, Umbel- 



98 



PART 



-ORGANOGRAPHY. 



lifer sb and Labiatss, the Geranium, Mallow, and many Lobelias 
and Campanulas. Figures 248 and 249 represent flowers of the 
common Pink, in different stages of development; in the former 





Fig. 248. 



Fig. 249. 



Fig. 248. 
Fig. 249. 



-Flower of Pink in the earlier or staminate stage of development. 
-Flower of Pink in the later or pistillate stage of development. 



the stamens are ripe, and shedding their pollen; while in the 
latter and older flowers they are past maturity and have with- 
ered, the expanded stigmas taking their place. It is evident that 
an insect which has visited the younger flower, and become dusted 




Fig. 250. Fig. 251. 

Figs. 250 and 251. — Staminate and pistillate stages, respectively of flowers of 
Epilobium angustifolium. 

with its pollen, could hardly fail, when visiting the older, to 
deposit some of it on the stigmas. 

Figs. 250 and 251 represent the proterandrous flowers of the 
Great Willow Herb, Epilobium angustifolium. The mode of cross- 
fertilization is analogous to that of the Pink just described. 



CHAPTER XII. — POLLINATION AND FERTILIZATION. 



99 



In Fig. 250, the stamens, which are ripe and protrude from 
the corolla, stand in such a position that an insect visiting the 
flower for its nectar must touch them and receive some of their 
pollen, but the style, crowned by the not yet unfolded stigma 
lobes, is curved back out of the way. Later, as shown in Fig. 251, 
the stamens, having shed all their pollen, wither and curve back 
upon the petals, while the style straightens out and the stigmas 
unfold, occupying about the same position as the anthers did 
before. It is clear that here, as in the Pink, an insect flying from 
a flower in the earlier to one in the later stage of development, 
will be likely to transfer pollen to the latter flower and fertilize it. 

Proterogyny is much less common, though interesting instances 





Fig. 252. Fig. 253. Fig. 254. 

Fig. 252. — Diagram of the inflorescence of Arum maculatum. The spathe is 
contracted near its middle, and the passage-way obstructed by stiff hairs which 
point downward. These, being flexible at their base, permit the ingress, but not 
the egress, of insects. The pistillate flowers are clustered at a, on the base of the 
spadix, while the staminate flowers are above, at b. The former mature first, 
and after the pollen is shed, the hairs wither, permitting the pollen-dusted insects 
to escape. 

Figs. 253 and 254 represent the pistillate and staminate stages, respectively, 
of the flower of Scrophularia nodosa. When the flower first opens, the stigma 
is mature, and in the way of a visiting insect ; after this has withered, the stamens 
curve upward, and the now ripened anthers occupy a position similar to that pre- 
viously occupied by the stigma. 



1G0 PART I. — ORGANOGRAPHY. 

are found in the Birthwort, in the Arum, in Scrophularia nodosa, 
and in some other plants. Fig. 252 is a diagram of the inflores- 
cence of the Arum. The large enveloping spathe is contracted 
near its middle, leaving but a narrow passageway to the cavity 
below, which encloses the separate masses of staminate and pistil- 
late flowers. This passageway is obstructed by stiff hairs, which 
point downward. These, being flexible at their base, are readily 
bent downward and afford but a slight obstacle to the entrance 
of insects, but they are not so easily forced upward from below, 
because pressure in that direction brings the distal ends of the 
hairs into contact with the side walls of the tube. The insects 
which enter are, therefore, imprisoned. The pistillate flowers are 
clustered at the base of the spadix, and reach maturity consider- 
ably earlier than the staminate ones which are clustered above 
them. After the stigmas have passed maturity, a drop of nectar 
is secreted at the bottom of the tube to compensate the flies for 
their imprisonment; the anthers, now ripened, shed their pollen 
in abundance; the insects' bodies become thoroughly dusted with 
it; and, lastly, the hairs that prevented their exit, wither, permit- 
ting them to fly away to some other inflorescence of the same kind, 
carrying with them the fertilizing pollen. 

Figs. 253 and 254 represent the pistillate and staminate stages, 
respectively, in the development of the flower of Scrophularia 
nodosa. The nectar is secreted in the base of the tube. In the 
younger or pistillate stage the stigma is exposed at the entrance, 
in such a position that a visiting insect must come into contact 
with it in order to reach the nectar; the unripe stamens are bent 
back out of the way. In the older or staminate stage the stigma 
lies withered on the lip of the flower, while the four anthers, now 
ripe, are exposed in the throat, dusting with pollen the insect that 
visits the flower. It is evident that a bee flying from an older to 
a younger flower must necessarily effect the cross-fertilization of 
the latter. 

(3) By the greater potency of foreign pollen. It has already 
been stated that in some cases pollen from the same flower is 
entirely ineffective. 

But even in cases where the flowers are capable of self-fertil- 
ization, the pollen from other plants is commonly " more effective 
than their own; and, as showy or nectar-bearing flowers are 
almost constantly visited by insects, the chances are that cross- 
fertilization will usually be effected. 



CHAPTER XII. — POLLINATION AND FERTILIZATION. 



101 



(4) By heteromorphism, or by the existence within the limits 
of the same species of flowers of different kinds. In some cases 
there are two different kinds of flowers, — one with short stamens 
and long styles, and the other with long stamens and short styles. 
Such flowers are called dimorphous. Figs. 255 and 256 represent, 
respectively, the long-styled and short-styled flowers of Mitchella 
repens. The flowers occur in pairs, usually grown together, more 
or less, at the base, as shown in the figures a, a. It will be seen 




Fig. 255. 



Fig. 256. 



Fig. 255. — a, two long-styled flowers of Mitchella repens. b, the tubular 
corolla of one laid open so as to show the stamens. 

Fig. 256. — a, two short-styled flowers of same species ; the styles are con- 
cealed in the tube of the corolla, while the stamens protrude, b, one of the 
corolla-tubes laid open to show the stigmas. 



that the stigmas of the left-hand pair stand at about the same 
level as the anthers of the right-hand one. The two different kinds 
of flowers invariably occur on different plants of the same species. 
The lower figures, 6, 6, represent a flower of each kind, with the 
corolla tube laid open to show the relative arrangement. It will 
be seen that a bee visiting one of the short-styled flowers will have 
her head dusted by pollen from the long stamens as she reaches 
to the bottom of the cup for the nectar, and that in passing to one 
of the long-styled flowers she will bring the same parts in contact 



102 



PART I. ORGANOGRAPHY. 



with the stigmas, and therefore probably deposit pollen upon them. 
At the same time, also, her proboscis is brought in contact with 
the short stamens in the tube, and its middle portion dusted with 
the adhesive pollen. If now again she visits a short-styled flower, 
some of this pollen will in all probability be left upon the stigma. 




Fig. 257. Fig. 258. 

Fig. 257. — Flower of the common Sage, in the staminate stage, visited by a 
bee. The fertile anther lobes are seen in contact with the insect's body, while 
the stigma is well out of the way, barely projecting from the upper lip of the 
corolla. 

Fig. 258. — Flower of the Sage in the pistillate stage, when the stamens have 
withered and the style lengthened, so as to occupy a position similar to that of 
the fertile anther lobes in the previous figure. 



In some other cases as in Lythrum salicaria, there are flowers 
of three different kinds, long-styled, mid-styled, and short-styled 
ones, which constitute a very effective means of cross-fertilization, 
by insect agency. Such flowers are called trimorphous. 

(5) By special contrivances. Many of these are exceedingly 
elaborate and wonderful. The flower of the common Sage is an 
illustration of one of them. The flowers are proterandrous, and 
are pollinated by bees. Fig. 257 represents one in the staminate 
stage visited by a bee; the stigma is out of the way, nearly con- 
cealed under the arching upper lip of the corolla, while the anther- 
lobes are in contact with the back part of the insect's body as she 
sips the nectar. Fig. 258 represents a flower of the same plant in 
the pistillate stage, when the anthers have discharged their pollen 
and the style has lengthened, unfolding its stigmatic lobes and 
occupying such a position as to come in contact with the back of 
the insect when she enters the flower. 

The flower has two stamens, separately represented in Fig. 259, 
inserted in the throat of the corolla in such a position that the 



CHAPTER XII. — POLLINATION AND FERTILIZATION. 103 

insect, in order to reach the nectar, must pass between them. 
Each anther has a long, curved connective, which is pivoted near 
its middle to the apex of the filament. One lobe, the upper one 
in the undisturbed flower, is fertile, and the other sterile. Fig. 259 
represents them as they are in their normal position, and Fig. 260 





Fig. 259. Fig. 260. 

Fig. 259. — Position of stamens of Sage, when undisturbed. 

Fig. 260. — Positions of anthers, when a bee passes between the stamens to 
reach the nectar. 

as they are when a bee passes between them, butting her head 
against the sterile lobes, pushing them forward and upward, and 
turning the fertile lobes backward and downward. It is evident 
that the insect visiting the flower in its staminate stage will get 
the back and upper portion of her hairy body dusted with pollen 
from contact with the fertile lobes, and in flying away to a flower 
which is in the pistillate stage, will bring the same part of her 
body into contact with the stigmas. 

Another interesting instance among the hundreds that might 
be mentioned occurs in Habenaria ciliaris, one of our most beau- 
tiful orchids. Fig. 261 represents one of the flowers of this plant. 
In the center of it is the column of combined pistils and stamens, 

a. The stigma lies centrally between the anthers, each of which 
produces a pollinium, which is club-shaped in form, and has at its 
lower end a sticky disc, as represented in Fig. 262. The delicately 
fringed lip is connected at its base with the long, tubular nectary, 

b, Fig. 261, which contains the honey secretion. The flowers are 
visited by butterflies, whose long tongues enable them to probe the 
bottom of the tube. In this process the visiting insect squeezes 
the thick basal portion of his tongue between the sticky discs of 



104 



PART I. — ORGANOGRAPHY. 



the pollinia, which adhere firmly, and are withdrawn from the 
anthers when he flies away. The pollinia, when first withdrawn, 
stand out nearly at right angles to the insect's tongue, but after a 
few moments, by a drying process which they undergo, they bend 
obliquely downward and somewhat inward, so that when the next 
flower is visited, they are brought into contact with the sticky 
stigmatic surface, and some of the pollen is almost inevitably 
deposited upon it. By flying thus from flower to flower, a consid- 
erable number may be fertilized before finally the pollinia are 
brushed off, or their pollen exhausted. 

While, as has been stated, cross-fertilization is the law, there 
are a few remarkable instances in which flowers appear to be 
constructed with special reference to self-fertilization. Some Vio- 
lets and Polygalas, for example, produce, besides showy flowers 
that are visited by insects, others that are inconspicuous, closed, 




B 




Fig. 261. 



Fig. 262. 



Fig. 261. — Flower of Habenaria ciliaris, with three rounded sepals, two strap- 
shaped petals which are fringed at the apex, a fringed lip with the base of which 
is connected a long tubular nectary, b ; a column, a, consisting of a stigma 
depressed between two anther-lobes, each of which contains a pollinium. c is 
the ovary of the flower. The flower is magnified about two diameters. 

Fig. 262, A and B. — A, Column of combined stigma and stamens, separated 
from the flower and more highly magnified, a, one of the anthers, the slit show- 
ing where the pollinium has been withdrawn ; b, the stigma ; c, opening into the 
nectary at the base of the labellum. B, The two pollinia still more highly magni- 
fied ; a, the mass of agglutinated pollen grains ; b, the sticky disc at the opposite 
end of the pollinium. 



and often partly concealed beneath the ground, so that insects 
cannot penetrate them, and in which the pollen falls directly upon 
the stigma and fertilizes it. Such flowers produce seed abun- 
dantly, and yet there is the closest of in-and-in breeding. They 



CHAPTER XII. — POLLINATION AND FERTILIZATION. 105 

appear to be a contrivance by means of which the plants are able 
to produce a greater multitude of seeds with a less expenditure 
of energy than by the production of an equal number of the ordi- 
nary flowers. They seem to multiply in this way as other plants 
do by means of bulblets or tubers, while the occasional crossing 
which occurs by means of the showy flowers serves to keep the 
stock vigorous. 

It does not come within the scope of this work to treat this 
subject more extensively, but those who are interested in it, and 
wish to pursue it further, should read some or all of the following 
works: Darwin's "Cross and Self Fertilization in the Vegetable 
Kingdom''; Sir John Lubbock's "British Wild Flowers in Relation 
to Insects"; Mueller's "The Fertilization of Flowers"; the portion 
of Kerner's "Natural History of Plants," and the chapter in Gray's 
"Structural Botany" which relate to this subject. 

Fertilization. By Fertilization is meant the process which 
takes place subsequent to the deposit of the pollen on the stigma, 
resulting in the union of the nuclei of the two reproductive cells, 
the male or sperm cell of the pollen and the egg cell of the ovule. 

Attention has already been directed to the fact that pollen 
grains are a form of spores, termed microspores, and that, like 
other spores, they possess the power of germination. The imme- 
diate stimulus to germination is usually supplied by the sticky 
secretion of the stigma, though in some instances the germination 
of the microspores begins before they have left the sporangia, 
which are here called anther sacs. This secretion of the stigma, 
which not only stimulates the germination of the pollen grain but 
also nourishes it during its growth, consists of a solution of sugar 
varying in strength in different species and suited to the growth 
of the pollen of that particular species; a fact which explains in 
part why pollen grains germinate best on the stigmas of flowers 
of the same species. During the course of germination, the nucleus 
of the pollen cell divides and two nuclei, known as the generative 
nucleus and the tube nucleus, are formed. See Fig. 263. The 
generative nucleus soon divides again, forming two male nuclei, 
which shortly become primordial male cells, sperms or male 
gametes. Meanwhile the pollen grain, nourished by the stigmatic 
secretion, has swollen and ruptured its outer coat and protruded 
its living contents, enveloped within the thin inner coat, thus 
forming the pollen tube. This growth is characteristic of the 
male gametophyte, which, though dependent, minute and usually 



106 



PART I. — ORGANOGRAPHY. 



short-lived, is the homologue of the independent and conspicuous 
gametophytes of the mosses. The pollen tube readily finds its way 
between the easily separable cells composing the loose, interior 
tissues of the style or through the tubular passage in the latter, if 
there be one, to the interior of the ovary 
and enters the micropyle of the ovule. 
See Figs. 264 and 265. In its descent 
the tube is assisted by the action of 
enzymes which it secretes and it is nour- 
ished by the cells along its path. It is 
evident that at least as many pollen- 
tubes will be required as there are ovules 
in the ovary, every ovule requiring one 
for its fertilization. 

The time that it takes for the pollen- 
tube to reach the ovule and effect its 
fertilization varies greatly in different 
plants. In some it occupies only a few 
hours, while in others it may require 
weeks, or even months, as in the Orchids. 
We have referred to the anther sacs 
as spore cases or sporangia and since the 
pollen grains have been termed micro- 
spores we might more accurately name 
the anther sacs microsporangia ; they are 
borne upon the microsporophylls or 
stamens. 

The ovules are likewise sporangia, and 
since they contain a larger spore, we may 
term them megasporangia; they are 
borne in megasporophylls or carpels. 

The megaspore, however, is not only 
larger than the microspore, but differs 
further in that it is not discharged from 
the sporangium but remains imbedded in 
the tissues of the nucellus. Upon the onset of germination the 
megaspore also enlarges, its nucleus divides into two nuclei which 
move to opposite ends of the spore, — here called the embryo sac, — 
while the central part is filled with water. 

These two nuclei again divide and the resultant four do like- 




Fig. 263. — Germinating 
pollen grain of Lilium 
martagon (after Stras- 
burger). A, antheridial 
mother-cell ; B, vegeta- 
tive nucleus. 



CHAPTER XII. — POLLINATION AND FEPvTILIZATION. 



107 



wise, giving eight nuclei, four at each end of the embryo sac. One 
nucleus from each group, the two polar nuclei, approach the centre 
of the embryo sac and there fuse into one. This completes the 
development of the female gametophyte, which is included within 
the embryo sac and like the male gametophyte is inconspicuous 
and 'parasitic. It now contains seven nuclei or primordial cells 
surrounded by cytoplasm. Toward the micropylar end of the sac. 




Fig. 264. 



Fig. 265. 



Fig. 264. — Diagram of flower in vertical section .to show fertilization of 
ovule: ca, calyx; co, corolla; st, stamen; p, pollen grain sending tube, t, down 
through the tissues of the style and into the micropyle of the ovule. In the 
nucellus of the ovule is seen the embryo-sac with the synergidae, oosphere, antip- 
odal cells and nucleus. 

Fig. 265. — Diagram representing an ovule in the process of fertilization : f, 
funiculus of the ovule penetrated by a spiral vessel ; ch, chalaza ; a, outer integ- 
ument, or primine ; b, inner integument, or secundine ; p, end of pollen-tube that 
has penetrated to the nucellus, n; e, embryo-sac; nu, nucleus of embryo-sac; 
s,s, the two synergidae ; o, the oosphere ; and ac, the antipodal sells. 



are three of these primordial cells ; the central one is known as the 
egg cell, oosphere, female cell or female gamete; the other two are 
named the synergidae; these three constitute the egg apparatus. 
Nearby is the fused nucleus, which becomes the primary endo- 
sperm nucleus, and at the other end of the sac are the three remain- 
ing primordial cells which soon become surrounded by cell walls 
and constitute the antipodal cells. (Fig. 265.) While the com- 
mon type of embryo sac is described above, let it be understood 



108 



PART I. — ORGANOGRAPHY. 



that other types containing sixteen, four, and even two nuclei are 
met with. 

The pollen-tube is guided to the micropyle, partly by various 
mechanical contrivances, such as by papillae on the placenta, by 
the position of the funiculi, etc., and partly, also, as it nears its 
destination, by the stimulating influence of a fluid which escapes 
from the synergidse. 

It enters the embryo-sac by dissolving its wall, the end of the 
pollen-tube ruptures, its sperm cells are discharged, one of these 
male gametes is attracted to the egg cell and fuses with it, forming 
the fertilized egg (oospore). The second sperm fertilizes the 
primary endosperm nucleus and the growth resulting gives rise to 




Fig. 266. 



Fig. 267. 




Figs. 266 to 269. — Diagrams represent- 
ing successive stages in the development 
of a dicotyledonous embryo. s. in each 
case is the suspensor or pro-embryo, and 
e, the embryo. In Fig. 268, the embryo 
is so far advanced that the first leaves, or 
cotyledons, c. c, may be recognized ; r, is 
the root, and a, the growing apex of the 
stem. 

the endosperm. From the fertilized egg the development of the 
embryo (sporophyte) begins. Some of the successive stages in 
the development of the embryo are roughly illustrated in the dia- 
grams, Figs. 266 to 269, inclusive. 

Cell division is by karyokinesis or indirect nuclear division (see 



CHAPTER XII. — POLLINATION AND FERTILIZATION. 109 

page 168), and at first takes place only in one plane, forming a 
chain or linear series of cells, technically called the suspensor. 
Then the terminal member of this chain, the embryo-cell, begins 
to divide in different planes, forming a mass of cells. As cell- 
division proceeds, the mass gradually becomes differentiated into 
the various organs of the embryo, a rudimentary root, a rudimen- 
tary stem and rudimentary leaves becoming recognizable. It is to 
be observed that the root end, or radicle, always points toward the 
micropyle of the ovule. 

The remarkable phenomenon known as Parthenogenesis, which 
consists in the development of an embryo by an unfertilized egg, 
is known to occur in but few species, chiefly Composite. 

As already stated, the endosperm originates with the union of 
the two polar nuclei and the subsequent fusion with a sperm from 
the pollen-tube; the nucleus resulting from this triple fusion 
divides, rapidly forming a great mass of free nuclei, which line 
the wall of the sac. Afterwards, these nuclei become complete 
cells by the development of cell- walls, and the further growth of 
the endosperm now goes on by cell-division, which proceeds from 
without inwards. This is the more usual process. Sometimes, 
however, the first division of the nucleus results in the formation 
of two perfect cells, and the development of the endosperm takes 
place from the very first by cell-division, and not by free nuclear 
division. In most cases, the embryo-sac enlarges very materially 
after fertilization and during the formation of the endosperm. 
Commonly, also, the cells of the latter and of the- embryo com- 
pletely fill it when the seed is mature, but there are instances, of 
which the Coconut affords a conspicuous example, where only the 
peripheral portion of the interior of the sac becomes cellular, 
while the interior remains fluid. The so-called "milk" in the 
Coconut, is the portion of the cavity of the embryo-sac which has 
failed to become cellular, while the "meat" that surrounds it is the 
endosperm. 

In most cases, as the embryo-sac and its contents develop, the 
cellular tissue outside it in the nucellus is absorbed and disappears ; 
but in some instances it remains or even increases in quantity, 
and is termed the perisperm. In the seeds of Canna, all of the 
nutritive tissue exterior to the embryo and within the seed-coats 
is perisperm. The seeds of the Peppers contain much perisperm 
and a comparatively small quantity of endosperm. Its use to the 
plant is the same as that of the endosperm, namely, to supply 



110 PART I. — ORGANOGRAPHY. 

food to the germinating embryo. The endosperm that is formed 
does not always remain until the seed is ripened, but not infre- 
quently, as in the Melon and Bean, it is completely absorbed by 
the growing embryo, and all within the seed-coats comes to consist 
of embryo. In a few cases, also, an endosperm is never developed 
at all. Beside the changes which take place in the interior 
of the nucellus as the result of fertilization, very important ones 
also occur outside of it. The ovary always increases in size; 
sometimes to a remarkable extent, and equally remarkable changes 
take place in the character and consistence of its walls. Compare, 
for instance, the ovary of the apple in flower with the ripened 
fruit, or the pistil of the cherry blossom with a ripened cherry. 
Moreover, organs exterior to the ovary feel the influence of the 
process. Even pollination is sufficient, in many caes, to cause the 
stamens and corolla to wither and fall away before the pollen- 
tubes have had time to reach the ovules. It is well known that 
the period of blossoming may be greatly prolonged in most flowers, 
if the pollen be prevented from gaining access to the stigmas. 
The results of the fertilization also often affect organs as far 
removed from the ovule as the calyx and receptacle, and even the 
bracts beneath the flower. Indeed, the influence is even more far- 
reaching than this, for the enormous development which the fer- 
tilized pistil undergoes, shows that all the nutritive processes in 
the plant must be more or less deeply affected. 

Practical Exercises. 

1. Compare the flowers of the Plantain, Indian Corn, Wheat, Timothy Grass 
and Hazel, all of them anemophilous, with the flowers of the Geranium, Pink, 
Apple, Buttercup, Poppy, or other entomophilous flowers, and note (1) the 
difference between the stigmas of the two groups as regards the extent of surface 
which they expose; (2) the difference as to the abundance and character of the 
pollen; (3) the difference in showiness, presence or absence of perfume, etc. 
(4) Observe in the Geranium whether the flower is proterandrous, proterogynous, 
or whether the maturing of the stigmas and anthers is simultaneous. (5) Observe 
different flowers of the Pink, and note the difference between the staminate and 
pistillate stages. (6) Ascertain Whether the anthers of the Buttercup dehisce 
extrorsely or introrsely, and state, if you can, what relation the facts you dis- 
cover bear to the cross-fertilization of the plant. 

2. Examine the flowers of the common Blue Flag; note the position of 
the nectar, the relative position of the anthers and stigmas, which way the 
anthers face, and the mode of their dehiscence, and determine, if you can, the 
manner in which cross-fertilization is effected. 

3. Examine the flowers of the common Barberry; observe the relative 
arrangement of the stamens and petals ; observe the structure of the anthers, 
and their mode of dehiscence ; by means of a pin irritate them slightly at the 
base, and observe the movement ; note the shape of the stigma, and the position 
of the nectar secretion ; if possible, observe the flower while it is being visited 
by an insect, and then explain its adaptations to cross-fertilization. 

Other interesting flowers to study for the same purpose are those of the 
Milkweed, the Cypripedium, the Pea, and the common Mallow. 

4. For autogamous flowers examine late in summer the runners concealed 



CHAPTER XIII. — THE FRUIT AND THE SEED. Ill 



underneath the leaves of Viola blanda, or of the English Violet (Viola odorata). 
Examine carefully their structure, and observe in those which have fruited the 
number of seeds produced. 

For the same purpose also study the autogamous flowers of Polygala poly- 
gama, and compare them carefully with the showy flowers of the same plant. 

5. Take the pistil of Datura Stramonium (or of some other flower whose 
ovary, style and stigma are rather large), and, immediately after the withering 
of the corolla, make thin, longitudinal sections through the stigma, style and 
ovary. Pollen grains will ordinarily be seen attached to the stigma, and pollen 
tubes may be traced into the style, particularly if the section be heated for a few 
moments in glycerine, so as to render the cells of the style as transparent as 
possible. The pollen tube may be distinguished by its more granular contents 
from the cells among which it has penetrated. 

If the sections are fortunately made, the pollen-tube may even be traced 
into the micropyle of the ovule. But if this cannot be done, some of the young 
ovules, if removed and carefully examined, will be found to contain the ends of 
pollen-tubes which have penetrated the micropyle and are in contact with the 
nucleus of the ovule. If the ovary of almost any species of the Orchidacae be 
cut open longitudinally a short time after the corolla has withered, numerous 
pollen-tubes will be seen, appearing under a magnifying glass as delicate, white, 
silky threads. The ovules of these plants are also favorable for the study of 
fertilization owing to their small size and the transparency of their parts. Other 
suitable plants for the purpose are the species of Pyrola, Monotropa, and Torenia 
Asiatica. 

6. To observe the growth of the pollen tubes, germinate fresh pollen grains 
(preferably Tradescantia, Begonia or Malva) in a ten per cent solution of sugar, 
prepared by boiling the solution for ten minutes so as to ensure sterilization, 
and transferring a drop of it with a sterilized needle to the center of a sterilized 
cover glass. Sprinkle a few pollen grains on this and invert the cover over a 
ring of the size of the cover or a little smaller, placed on a slide and held in 
place by a drop of water around its inner edge. Keep in a warm place (pre- 
ferably a moist chamber) for a few hours and examine with the high power of 
the microscope. The slide may be kept for several days and the growth of the 
pollen tubes observed from time to time. 



CHAPTER XIII.— THE FRUIT AND SEED. 
I. — The Fruit. 

The fruit consists essentially of the ripened pistil or pistils, but 
it may also include other organs which grow fast to these in the 
process of their development. 

Its structure, in a general way, resembles that of the pistil 
from which it is derived. The modifications which it undergoes in 
its development, in many cases at least, have reference to the 
dispersion of the seeds when they are ripened. 

The kinds of modifications that may take place are chiefly the 
following : 

(1) The loculi or compartments in the ovary, may decrease 
in number, as in the fruit of the Oak, which in flower is three- 
celled, but in ripening becomes one-celled. The similar case of 
the fruit of the Buckeye is illustrated in Figs. 270 and 271. The 
former figure represents a cross-section of the pistil at the time 
the flower is in full blossom when it contains three cells with two 



112 



PART I. — ORGANOGRAPHY. 



ovules in each cell, and Fig. 271 represents the same at a con- 
siderably later period of development, showing the almost complete 
abortion of two of the cells and of all the ovules but one. 

(2) An increase in the number of loculi sometimes takes 
place from the formation of false partitions, as illustrated in the 
capsule of Stramonium, which in flower is two-celled, but in fruit 
becomes four-celled. Fig. 272. 

(3) Alterations in the character of the surface may take 
place, as is also illustrated in Stramonium, whose pistil, when in 




Fig. 270. 



Fig. 271. 



Fig. 270. — Ovary of Buckeye when in Flower, cut transversely, showing 
three loculi and two ovules in each loculus. 

Fig. 271. — Ovary of Buckeye, cut transversely at a later stage of development, 
showing one ovule strongly developed, while the others have ceased their growth. 



flower, has only a soft, hairy covering, but in fruit is densely 
covered with sharp prickles; or in the Maple, whose pistil in 
flower is merely two-lobed, but, in fruit, develops on each lobe a 
prominent wing-like appendage, as shown in Fig. 273. 

(4) Alterations in the consistency of the ovary wall may 
take place. These may be of different kinds: (a) They may 
become thin and papery, as in the Bladder-senna; (b) hard and 
bony, as in the pericarp of many capsules; (c) tough and leathery, 
as in the rind of the Orange and Lemon; (d) hard without and 
soft within, as in the fruit of the Gourd; (e) soft without and 
hard within, as in the fruit of the Peach and Cherry; or (f) suc- 
culent throughout, as in the Gooseberry and Grape. 

(5) Organs external to the pistil, but more or less connected 
with it, often persist and become a part of the fruit. The calyx 
of the Wintergreen, for instance, grows fleshy, envelops the cap- 
sule, becomes red in color, and constitutes the edible portion of 
the fruit; in Clematis the style persists, becomes long and feathery, 



CHAPTER XIII. — THE FRUIT AND THE SEED. 



113 



and serves to waft away the ripened fruit; in the Strawberry the 
receptacle becomes thick and succulent, and constitutes the edible 
portion of the fruit, and in the Dandelion and Thistle the modified 
calyx-limb, or pappus, renders the fruit buoyant and easily wafted 
by the wind. 

Doubtless the reason why fruits often have conspicuous colors 
is to render them attractive to birds and other animals that can 
aid in their dispersion. As the seeds of edible fruits are usually 
indigestible, or difficultly digestible, the fact that the fruits are 





Capsule of Stramonium. 



Fig. 273. — Double Samara of Maple. 



pleasing to the taste aids the dispersion of their seeds, and secures 
their deposit under conditions favorable to germination. The 
hooks and spines which are found on many fruits, or attached to 
accessory organs, are also means by which plants utilize animals 
for the dispersion of their seeds. 

Dispersion.— The agencies made use of by nature for the dis- 
persion of fruits and seeds may be classified as follows: 

(1) The Wind, as when they acquire thin and flattened forms, 
or are provided with membranous expansions called wings, or 
have a feathery, hairy or parachute-like pappus, or are otherwise 
rendered light and buoyant. 

(2) Water Waves or Currents, as in the case of the Coconut, 
which, by its structure, is rendered buoyant, and by reason of its 
possessing a fibrous husk, and a thick, hard shell, is enabled to 
resist for a long time the action of salt water. 

(3) Explosive Mechanisms. In this manner the seeds of the 
Squirting Cucumber, Ecballium Elaterium (Fig. 274), are dis- 
charged. Many explosive mechanisms are due to Hygroscopism, 



114 



PART I.— ORGANOGRAPHY. 



the property possessed by some fruits, by which one part either 
absorbs water more rapidly than another, or parts with it more 
readily, thus in some cases causing a strain upon and at last a 
sudden rupture of the pericarp, scattering the seeds, or else giving 
rise to movements of a different character which are serviceable 
in placing the fruit or seed in conditions favorable to germination. 
To hygroscopism is attributable the violent bursting of the large 
capsules of the tropical Sandbox tree, Hum crepitans, Fig. 275. 
When the fruit is thoroughly ripe the segments suddenly separate 
with a loud report resembling that of a pistol, and the seeds are 
thrown out with a force which often projects them to the distance 





Fig. 275. 

Fig. 274.— Fruit of the 
Squirting Cucumber dis- 
charging its seed. 

Fig. 275.— Capsule of Sand- 
box tree, Hura crepitans. 



Fig. 274. 



of many yards. The capsules of. the well-known Touch-me-not, 
dehisce with violence from the same cause; and by reason of their 
hygroscopic properties the awns of some grasses twist and untwist 
as the quantity of moisture in the air changes, and in some 
instances the motion thus produced is utilized to drive the fruit 
into the soil. This is the case with the western Porcupine Grass. 
In some flowerless plants the same property is taken advantage 
of for the dissemination of the spores. The hygroscopism of the 
elaters of Equisetum, and some Liverworts, for example, is the 
means of ejecting the spores from their cases, and so of scattering 
them to the wind to be sown far and wide. 

(4) Animals. There are many ways in which plants make 
use of animals for the dispersion of their fruits and seeds. It 
has already been suggested that this is one of the reasons why 



CHAPTER XIII. — THE FRUIT AND THE SEED. 



115 



the fruits of some plants have become edible. Birds and frugivor- 
ous mammals are certainly, for this reason, among the most 
important adjuncts in the distribution of plants. By sparrows 
and squirrels, doubtless, whole forests have been planted. The 




Fig. 276. 



Fig. 277. 



Fig. 276. — Fruit of Martynia, considerably reduced. When ripe its beak 
splits into two sharp, hooked hard horns, by means of which it clings to the tails 
of cattle and horses, and the seeds are thus scattered. 

Fig, 277. — Fruit of Bidens connata, magnified about five diameters. 



showiness of many ripe fruits is also unquestionably an important 
aid to the dispersion of their seeds, as it attracts the attention of 
fruit-eating animals, and causes the fruits to be eaten, or at least 
to be plucked and tasted. But many fruits and seeds are provided 
with hooks, spines, barbs, adhesive pericarps, or other means by 
which they cling to the bodies of animals, and are thus scattered. 
Fruits of the Burdock, Bidens, Stickseed, Tick-trefoil and Mistle- 
toe are illustrative examples, and many others might be educed. 
Figs. 276 and 277 represent, respectively, the fruits of species of 
Martynia and Bidens. 

Classification of Fruits. — Although the following scheme of 
classification does not claim completeness, it includes the most im- 
portant forms of fruits, and for practical purposes will be found 
convenient. 



116 



PART I. — ORGANOGRAPHY. 



Fruits are primarily divided into two groups, those which are 
the product of a single flower, and those which are the product 
of a flower cluster. 

The former kind are subdivided into those which are the 
product of one pistil (either apocarpous or syncarpous), and 
those which are the product of more than one. The former of 
these subdivisions is divided into indehiscent forms, or those which 
do not split open when ripe, and dehiscent forms, those which do. 
The most important of the indehiscent forms are the following: 

(1) The Akene or Achenium. This is a one-seeded, dry, hard, 
seed-like fruit, like that of the Ranunculus, shown in longitudinal 




Fig. 278. 



Fig. 279. 



Fig. 280. 



Fig. 281. 



Fig. 278. — Superior achenium of Ranunculus, with portions of ovary wall 
removed to show internal structure. 

Fig. 279. — Inferior achenium of Sow Thistle. 
Fig. 280. — Caudate achenium of Clematis. 
Fig. 281. — Utricle of Chenopodium. 

section in Fig. 278. The akene may either be superior, or free 
from an adhering calyx, as in the above example, or it may be 
inferior, that is, having the calyx closely adherent, as in the fruit 
of the Sow Thistle and other Composite, Fig. 279. Fig. 280 repre- 
sents the caudate or tailed achenium of Clematis. 

(2) The Utricle. This is similar to an akene, but the pericarp 
is bladdery and fits the seed loosely; for example, the fruit of 
Chenopodium, Fig. 281. 

(3) The Caryopsis. This resembles the akene, except that the 
pericarp closely adheres to the seed, as in the Wheat, Indian Corn, 
Oat, etc., Fig. 282. 

(4) The Samara. This resembles an akene, except that it 
possesses a wing-like appendage. Fig. 283 represents the samara 
of the Ash, Fig. 284 that of the Elm, and Fig. 273 the double 
samara of the Maple. 



CHAPTER XIII. — THE FRUIT AND THE SEED. 



117 



(5) The Glans, or nut. This is a fruit, like that of the Oak 
or Hazel, with a thick, hard pericarp, enclosed, or partly so, in 
an involucre, Fig. 285. In the case of the Acorn, the involucre 




Fig. 282. 





Fig. 283. 



Fig. 284. 



Fig. 285. 



Fig. 282. — Caryopsis of the Oat. 
Fig. 283. — Samara of the Ash. 



Fig. 284. — Samara of the Elm. 
Fig. 285.— Glans of the Oak. 



consists of a cup-shaped expansion of the axis covered by closely 
imbricated scales, and is called the cupule. 

(6) The Cremocarp. This is the peculiar double fruit pro- 
duced by umbelliferous plants. Each mericarp, or half of the 
fruit, structurally resembles an inferior akene, but is longitudi- 





Fig. 286. 



Fig. 287. 



Fig. 288. 



Fig. 286. — Cremocarp of Fennel, splitting into two mericarps. 
Fig. 287. — Sectional view of drupe of Cherry; e, exocarp ; 
endocarp, and s, seed. 
Fig. 288. — Berry of Belladonna. 



mesocarp ; 



nally ribbed, and there are usually oil tubes between the ribs. 
Fig. 286 represents the cremocarp of Fennel. 

(7) The Drupe. This is a one-carpelled fruit like that of the 
Plum, Cherry and Peach, and is often called a stone fruit. In it 



118 



PART I. — ORGANOGRAPHY. 



the wall of the pericarp is differentiated into three portions, the 
outer or "skin," called the epicarp, the middle or succulent portion, 
the mesocarp, and the inner portion or hard wall enveloping the 
seed, the endocarp or putamen. Fig. 287 represents the drupe of 
the Cherry in longitudinal section. 

(8) The Try ma. This is a fruit structurally resembling the 
drupe, but the mesocarp is harder, more fibrous, the outer husk in 
most cases ultimately dehiscent, and the cavity containing the seed 
is usually more or less distinctly two-celled. The fruits of the 
Hickory, Walnut and Pecan are illustrations. See Fig. 289. 

(9) The Berry. This is a fruit which has a thin, membranous 
rind, and all the rest of the pericarp is succulent. The fruits of 




Fig. 289. 



Fig. 290. 



Fig. 291. 



Fig. 289. — Tryma of the English Walnut, with portion of sarcocarp removed. 
Fig. 290. — Fruit of Lemon, cut transversely, illustrating a hesperidium fruit. 
Fig. 291. — Cucumber, cut transversely, illustrating pepo fruit. 



the Belladonna, Grape and Gooseberry are illustrations. Berries 
may be one-, two- or even many-celled, and they may be either 
from an enlarged and juicy pistil or from one which has a sur- 
rounding receptacular cup. In the former case the berry is called 
superior, in the latter inferior. Fig. 288 represents the berry of 
Belladonna. 

(10) The Hesperidium is a fruit like the Orange, Lemon and 
Lime. It resembles a superior berry, but differs from one in hav- 
ing a leathery rind containing numerous oil glands. See Fig. 290. 

(11) The Pepo. This is a fleshy fruit like that of the Gourd, 
Melon and Cucumber, having a hardened or tough rind, Fig. 291. 

(12) The Pome. This is a fleshy fruit, the chief bulk of 
which consists of adherent, fleshy calyx-tube or receptacle, as the 
Quince, Pear and Apple, Fig. 292, 



CHAPTER XIII. — THE FRUIT AND THE SEED. 



119 



The more important dehiscent fruits which are the product 
of a single pistil are the following: 

(1) The Follicle. This is a one-carpelled, dry fruit, that 
dehisces along the ventral suture, as the fruit of the Columbine, 
Fig. 293. 

(2) The Legume. This differs from the follicle only in the 
fact that the dehiscence takes place along the dorsal as well as 
the ventral suture, forming two valves. This form of fruit is 




Fig. 292. 





Fig. 294. 



Fig. 292. — Sectional view of a pome, the fruit of the Apple. 
Fig. 293. — Follicle of the Columbine. 
Fig. 294. — Legume of the Pea. 

common in the Pulse family. The Pea-pod, Fig. 294, is an illus- 
tration. 

(3) The Loment. This is a modification of the legume, which, 
instead of dehiscing longitudinally, breaks up transversely into 
segments, as the fruit of the Meibomia, Fig. 295. 

(4) The Cochlea is a coiled legume like that of the Medicago, 
Fig. 296. 

(5) The Capsule differs from the dehiscent fruits above de- 
scribed in consisting of two or more united carpels. In this form 
of fruit, several modes of dehiscence are observed. The rupture 
of the pericarp may take place along the sutures of the carpels, 
as is more commonly the case, or independently of them; if the 
dehiscence is sutural, it may be along the marginal sutures only, 
along the dorsal sutures only, or along both; the splitting may be 
complete or only partial, and it may begin either at the apex or 
at the base. Sometimes the valves, in separating, carry the pla- 
centae with them, at other times the latter are left behind, forming 



120 



PART I. — ORGANOGRAPHY. 



a central column, which is technically called the columella. The 
following are the commonest kinds of capsular dehiscence: (a) 
The septicidal, in which splitting takes place along the septa, or 
partitions, as in Fig. 297. (b) The septifragal, where the valves 
break away from the septa, as in Fig. 298. (c) The loculicidal, 




Fig. 295. 

Fig. 295. — Loment of Mei- 
bomia 

Fig. 296. — Cochlea of Med- 
icago. 




Fig. 296. 



where the carpels open by their dorsal sutures into the loculi or 
cavities of the cells, as in Fig. 299. (d) The marginicidal, when 
the valves break away along the line where the septa join the 
outer wall, Fig. 300. All these are forms of valvular dehiscence. 





^x 



Fig. 297. 



Fig. 298. 



Fig. 299. Fig. 300. 



Fig. 297. — Diagram of the septicidal dehiscence of a capsule. 

Fig. 298. — Diagram of the septifragal dehiscence of a capsule. 

Fig. 299. — Diagram of loculicidal dehiscence of a capsule. 

Fig. 300. — Diagram of marginicidal dehiscence of a capsule. 

The Violet and Gentian afford examples in which the valvular 
dehiscence is complete, as shown in Fig. 301, while in the capsule 
of Lychnis, Fig. 302, it is partial or incomplete, and the partial 
separation takes place at the top of the capsules. In the capsules 



CHAPfER XIII. — THE FRUIT AND THE SEED. 



121 



of the Hare-bell and of Cinchona Calisaya, see Fig. 303, it occurs 
at the base, (e) The porous. In this form, Fig. 304, the dehis- 
cence takes place by small openings or pores, as in the Poppy. It 
is really a variety of the valvular dehiscence, (f) The circum- 
scissile is that form in which the upper portion of the capsule 




Fig. 301. 



Fig. 302. 



Fig. 303. 



Fig. 304. 



Fig. 301. — Capsule of the Gentian, dehiscing septicidally into two halves. 

Fig. 302. — Capsule of Lychnis, showing partial dehiscence of capsule. 

Fig. 303. — Basally dehiscent capsule of Cinchona Calisaya. 

Fig. 304. — Capsule of the Poppy, showing porous dehiscence. 

separates from the lower, like a lid, by a transverse dehiscence, as 
in the capsule of Hyoscyamus, Fig. 305. Such a capsule is often 
termed a pyxis, (g) The irregular, or that form, in which the 






Fig. 306. 



Fig. 307. 



Fig. 308. 



Fig. 305. — Pyxis of Hyoscyamus. 

Fig. 306. — Silique of Celandine 

Fig. 307. — The dehiscing silicle of Shepherd's Purse. 

Fig. 308. — Sorosis of the Mulberry. 



dehiscence takes place in an indefinite manner or by an irregular 
rupture of the pericarp, as in the garden Snap-dragon. 

The following capsules have peculiarities which make it conven- 



122 



PART I. — ORGANOGRAPHY. 



ient to apply special names to them: One which is elongated, 
two-valved, and the valves of which separate from the base 
upward, leaving the seed-bearing placentas in place, as in the 
Mustard and Celandine, Fig. 306, is called a silique.; and a short- 
ened silique, like that of Shepherd's Purse, Fig. 307, is termed a 
silicle. 

Fruits that are the product of one flower, but of many separate 
carpels, are called aggregate fruits. 

An aggregate fruit that consists of a collection of small drupes, 






Fig. 309. 



Fig. 310. 



Fig. 311. 



Fig. 309. — Syconium of the Fig, shown in longitudinal section. 
Fig. 310. — Strobile, or cone of Pine. 
Fig. 311. — Galbulus of Juniper. 



like that of the Blackberry and Easpberry, is called an etaerio. 
A strawberry is an aggregation of akenes on a thickened and 
succulent conical or convex receptacle. A hip is an aggregation 
of akenes on a thickened and succulent hollow receptacle. The 
term is applied to the fruit of the Rose. 

Fruits that are the products of flower-clusters instead of single 
flowers are termed collective or multiple fruits. The most impor- 
tant are the following: 

(1) The Sorosis. This is a fruit like those of the Mulberry, 
Fig. 308, and Pineapple, where the inflorescence in ripening has 
become fused together into a compact mass. 

(2) The Syconium. This is the peculiar fruit of the Fig, the 
edible portion of which consists of a succulent, hollow receptacle, 
which incloses a multitude of akene-like nuts, each the product of 
a distinct flower, Fig. 309. 



CHAPTER XIII. — THE FRUIT AND THE SEED. 



123 



(4) The Strobile, or Cone. This is a multiple dry fruit con- 
sisting of a scale-bearing axis, each scale enclosing one or more 
seeds; for example, the cones of the Hop and Pine, Fig. 310. 

(4) The Galbulus. This is a cone, the scales of which have 
become succulent. The so-called Juniper Berry, Fig. 311, is an 
example. 



Fruits. 



Product of 
a Single 
Flower. 



j Product of a 
Flower- 
^ Cluster. 



Recapitulation of Fruits. 



One Pistil. 



Indehiscent 
Fruits. 



Dehiscent 
Fruits. 



More than 
I One Pistil. 
) Multiple or 
i Collective Fruits 



Aggregate 
Fruits. 



fThe akene, utricle, cary- 

j opsis, samara, glans, 
\ cremocarp, drupe, tryma, 
I berry, hesperidium, pepo 
[and pome. 

J" Follicle, legume, loment, 
■s cochlea, capsule, silique, 
(silicle and pyxis. 

( Etaerio, strawberry and 
thip. 

j Sorosis, syconium, stro- 
( bile and galbulus. 



II.— The Seed. 

The seed is the fertilized and ripened ovule. It ordinarily 
remains enclosed within the ovary, and is nourished by it until 
maturity, though the rule has some exceptions. As might have 
been expected, also, the seed ordinarily bears a general resem- 
blance to the ovule from which it is derived. For example, the 
coats usually remain to form the coats of the seed; the chalaza 
and micropyle of the ovule are still recognizable and are called 
by the same names in the seed; the raphe, if present in the 
former, is also present in the latter; the position of the seed in 
the ovary corresponds to that of the ovule; the terms atropous, 
campylotropous, etc., apply equally well to the seed, and the 
latter, when ripe, breaks away from the funiculus, if that organ 
is present, or if not, from the placenta, leaving a scar called the 
hilum, which corresponds to the part called the hilum in the ovule. 
But notwithstanding the structural resemblance in many particu- 
lars, the ovule undergoes important changes, not only in size but 
also in form and structure, in the course of its development into 
seed. Among the most important of these are the following: 

(1) The seed-coats, particularly the outer, frequently undergo 
considerable modification, While the exterior one of the ovule 



124 



PART I. — ORGANOGRAPHY. 



is thin, membranous and smooth, that of the seed, termed the testa 
or spermoderm, is usually considerably thickened, and acquires 
various markings or appendages. 

If the testa becomes very thick, hard and resistant, it is 
termed crustaceous; if smooth and shining, it is described as pol- 
ished; if roughened, it may be tuberculate, pitted, rugose, reticu- 
late, alveolate, fissured, furrowed, hairy, etc.; and if appendaged, 
the appendages may be in the form of a coma, or long hairs, which 
nearly or entirely cover the seed, as in the Cotton, or only one end 




Fig. 312. 




Fig. 313. 



Fig 314 



Fig. 312. — Comose seed of the Milk-weed. 
Fig. 313. — Alate or winged seed of the Catalpa. 
Fig. 314. — Alate seed of the Pine. 

Fig. 315. — Fruit of Nutmeg, with one side removed, 
enveloped in the mace. 



Fig. 315. 



to show the seed 



of it, as in the Milkweed, Fig. 312 ; or the appendage may be in the 
form of short silky hairs, as in the seeds of Nux Vomica ; of or one 
or more flattened expansions, called wings, as in the seed of the 
Catalpa, Fig. 313, and of the Pine, Fig. 314; or it may be an out- 
growth from the funiculus or placenta, which more or less com- 
pletely envelops the seed, and constitutes the aril, as in the mace 
of the Nutmeg, Fig. 315, the aril of the Water-lily, and that of 
Celastrus scandens; or, lastly, it may be in the form of a cellular 
excrescence at the hilum or along the raphe, called the caruncle, 
or crest, as in the seed of Sanguinaria, Fig. 316. Not infrequently, 
also, the outer portion of the testa undergoes changes into muci- 
lage, as in the seeds of the Quince and Flax. 

The inner coat of the seed, called the tegmen or endopleura, is 
sometimes wanting; sometimes it coalesces with the outer coat 



CHAPTER XIII. — THE FRUIT AND THE SEED. 



125 



and becomes indistinguishable from it. When present, it is usually 
thin and membranous. 

(2) The internal structure of the nucellus undergoes impor- 
tant changes. Some of these were mentioned under the subject 
of fertilization. It is replaced in the seed by the kernel. 

The kernel of the seed, or that portion within the seed-coats, 
may, as we have already seen, consist either entirely of the 






Fig. 316. 



Fig. 317. 



Fig. 318. 



Fig. 316. — Carunculate seed of the Blood-root. Magnified. 
Fig. 317. — Longitudinal section of acorn, showing the exalbuminous seed. 
Fig. 318. — Albuminous seed of Hyoscyamus, shown in longitudinal section. 
Magnified. 



embryo, in which case it is described as exalbuminous, as in the 
Acorn, Fig. 317, or of the embryo, together with more or less 
nourishing matter called, according to its origin, either endosperm 
or perisperm, in which case the seed is termed albuminous, as in 
Fig. 318, which represents a section of the seed of Hyoscyamus. 
The term endosperm, as already explained, is applied to the 
nutritious matter developed outside the embryo but within the 
embryo-sac, while perisperm is applied to the nutritious matter 
stored up outside of the embryo-sac. Both serve the same pur- 
pose, and in the fully developed seed it is often difficult, if not 
impossible, to distinguish them. 

In albuminous seeds the amount of endosperm differs very 
widely, and in describing it, it is usual to compare its quantity 
with that of the embryo. If much greater it is copious, or abun- 
dant; if about the same, equal; and if comparatively small in 
quantity, scanty. 

The texture of the endosperm differs, also, in different seeds. 
In some, like the Wheat and Buckwheat, it is farinaceous, or 
mealy; in the seeds of Barberry and Coconut, it is of a denser 
consistency, yet readily cut with a knife, and is called fleshy; in 
some, as the seeds of Poppy and Bloodroot, it is oily; in the seeds 



126 



PART I. — ORGANOGRAPHY. 



of Nux Vomica and many others is is horny; in others still, as 
that of the Ivory Palm, it is so exceedingly hard as to be appro- 
priately called bony; and in the seed of the Nutmeg, since it has 
an uneven or marbled appearance, and is more or less fissured 
transversely, it is called ruminated. 

The Embryo. This is the essential part of the seed; it is the 
young plant which is the end and purpose of the entire flower and 
fruit; it is the finished product of the reproductive process. 

In exalbuminous seeds it is usually well developed, while in 
albuminous ones it is apt to be smaller, and have its parts less 
perfectly formed, but this general rule has many exceptions. 

As respects the position of the embryo in the seed, it has 
already been noted that the radicle always points to the micropyle. 
As regards its position with reference to the endosperm, this varies 
greatly in different seeds. In the seed of the Violet, Fig. 319, it is 
straight, and buried in the endosperm. This is true, also of the 
relatively smaller embryo of Nux Vomica, Fig. 320 ; in the seed 
of Hyoscyamus, already mentioned, it is curved within the endo- 
sperm ; in the seed of Lychnis dioica, Fig. 321, it is curved, but lies 






Fig. 319. 



Fig. 320. 



Fig. 321. 



Fig. 319. — Seed of Violet, showing straight embryo buried in the endo- 
sperm. Magnified. 

Fig. 320. — Seed of Nux Vomica, with one side removed, showing position of 
embryo. About natural size. 

Fig. 321.— Seed of Lychnis dioica, showing embryo curved around the endo- 
sperm. Magnified. 



on the outside of it, and almost completely surrounds it, while in 
the Indian Corn, Fig. 322, it is placed to one side of it. 

An embryo that is well developed, like that of the Bean, Figs. 
323 and 324, possess four parts: an initial stem, termed the 
caulicle or hypocotyl; at the lower end of this the beginning of the 
root, called the radicle; near the upper end of the caulicle two 
thickened bodies more or less resembling leaves and homologous 
with them, the cotyledons; and between these a small bud called 



CHAPTER XIII. — THE FRUIT AND THE SEED. 



127 



the plumule. Thus, in the embryo, all the organs of vegetation 
are already present. 

The cotyledons, although in their nature leaves, and sometimes 
doing for a time the work of foliage, as those of the Maple and 
Morning-glory, are commonly thickened and surcharged with 
nourishment which serves to feed the growing plantlet; in many 



— d 





d 



Fig. 322. 



Fig. 323. 



Fig. 324. 



Fig. 322. — Seed of Indian Corn, showing embryo placed to one side of the 
endosperm. The outer portion of the embryo forms a surrounding sheath known 
as the Scutellum. 

Fig. 323. — Embryo of Bean. 

Fig. 324. — The same, with one of the cotyledons turned back to show the 
plumule, a, the caulicle ; b, the radicle; c, the plumule; d and d', the cotyledons. 



instances this function is the only one they discharge. This is the 
case with the embryos of the Pea and Oak. In these instances 
they do not rise above the soil at all in germination, but remain 
buried in the ground until their supply of nutriment has been 
exhausted by the growing seedling, when they decay and dis- 
appear. Such cotyledons are described as hypogeous, while those 
which rise above the soil are called epigeous. 

Embryos like those of the Bean, because they possess two 
opposite cotyledons, are called dicotyledonous. Not all embryos, 
however, are constructed on precisely this plan. Some, as those 
of Lilies, Sedges and Grasses, have the leaves alternate from the 
start, and usually the lower one is much the most highly devel- 
oped, and being the only conspicuous one, besides being folded 



128 PART I. — ORGANOGRAPHY. 

about the rest and concealing them from view, the embryo is called 
mo?wcotyledonous. Fig. 325 represents the monocotyledonous em- 
bryo of Indian Corn. The embryos of some other plants, particu- 
larly of many members of the Pine family, have more than two 
cotyledons in a whorl — sometimes as many as fifteen; embryos of 
this kind are described as polycotyledonous. Fig. 326 represents 
the germinating embryo of a species of Pine. There are a few 
cases in which the cotyledons are aborted or wanting. Such em- 
bryos have been called acotyledonous. The seed of the common 
Dodder contains an embryo of this kind. There is reason to be- 
lieve, however, that it was once dicotyledonous, for the affinities of 
that plant, as shown by the structure of its flowers, are with Dico- 
tyledons. The plant is, however, a parasite, and, doubtless, the 
loss of its cotyledons bears some relation to its parasitic habits. 
Probably once, like its near relative, the Morning-glory, it pos- 





Fig. 325. 

Fig. 325. — Monocotyledonous em- 
bryo of the Indian Corn. 

Fig. 326. — Polycotyledonous em- 
bryo of a species of Pine. (After 
Sachs.) 



. Fig. 326. 

sessed foliage, and obtained its living in a legitimate way, but 
having acquired the parasitic habit (a habit degrading to plants, 
animals and men), and having no use for foliage of its own, it 
lost its leaves, and the degradation of form came, finally, even to 
affect the embryo and cause the loss of its cotyledons. These 
probably were once highly developed and did partial duty as 
foliage, as those of the Morning-glory still do. 

There are a few instances, also, where plants whose actual 
affinities are with Dicotyledons,, possess but one cotyledon, the 



CHAPTER XIII. — THE FRUIT AND THE SEED. 



129 



other having become aborted, the embryos thus becoming falsely 
monocotyledonous. 

The distinction between monocotyledonous and dicotyledonous 
embryos is, with these exceptions, one of fundamental importance, 
— one of the great divisions of the flowering plants, the Monocoto- 
lydons, being characterized by monocotyledonous embryos, and 
another, the Dicotyledons, by dicotyledonous ones. 

The individual cotyledons may be folded or bent in various 






Fig. 327. 



Fig. 328. 

Fig. 327. — Embryo of Basswood, showing lobed cotyle- 
dons. Magnified. 

Fig. 328. — Diagram illustrating accumbent cotyledons. 
Fig. 329. — Diagram showing incumbent cotyledons. 



ways in the seed, as leaves are in the bud, and their folding may 
be described in the same way. They also have a variety of shapes, 
the same as ordinary leaves, though they are much more commonly 
entire. Occasionally, however, we find them toothed 0¥ lobed, as 
in the embryo of the Basswood, Fig. 327. 

Although we often find the embryo straight, or the caulicle 
lying in the same line as the cotyledons, in many seeds it is bent 
so as to lie alongside of them. In this case it may be applied to 
their edges, as shown in the diagram, Fig. 328, which represents 
a cross-section through the cotyledons and caulicle, in which case 
it is described as accumbent; or it may be applied to the outer 
face of one of them, as in Fig. 329, when it is described as incum- 
bent. An illustration of the former arrangement occurs in the 
seed of the garden Candy-tuft, and of the latter in the seeds of 
Shepherd's Purse. 

The number of seeds produced by some plants is enormously 
great. A single Poppy capsule, according to Cooke, has been 
known to contain as many as forty thousand seeds, and the Poppy 
is certainly much less prolific than many other flowering plants. 
If all the seeds of almost any ordinary tree were to germinate and 
reach maturity, and the seeds of all these in turn were to develop, 
but a few generations would suffice before the earth would be so 



130 PART I. — ORGANOGRAPHY. 

crowded with them that no room would be left for other plants. 
But, as a matter of fact, only a few of the large number of seeds 
produced by a plant ever reach maturity. The young plant 
has to contend with a thousand enemies, in the form of destructive 
insects, beasts and fellow plants; it must often wage war, also, 
against unfavorable conditions of soil and climate, against heat 
and cold, wet and drouth, and be hampered by the shadows cast 
by its older and -stronger brethren. It is fortunate if, in the bitter 
struggle for existence, it survives to help gladden the earth with 
bloom and verdure, for the great majority perish, 



Practical Exercises. 

1. Study the following fruits, and classify and name them according to the 
system given you in this, chapter : The Watermelon, the Banana, the Raspberry, 
a grain of Corn, the Butternut, the Almond, the Osage Orange, the Plum, the 
Sunflower fruit, the fruit of the Locust, that of Stramonium, of Red Cedar, of the 
Carrot and of the Beet. 

2. Study the following fruits with reference to their adaptations for disper- 
sion : The fruit of Dog-bane, of the wild Plum, of Agrimonia, of the wild 
Geranium, of the Elm, of Cleavers, of the Clot-bur, of the garden Balsam, of the 
Wild Cucumber (Echinocystis), of the Grape and of the Hound's-Tongue. 

3. Examine seeds of the following plants with reference to the surface 
markings, the coats, the position of the hilurh, the micropyle and the raphe : 
The Bean, the Pea, the Pumpkin, the Almond, the Stramonium and the Nux 
Vomica. 

4. Soak the following seeds for twenty-four hours in tepid water ; then 
remove the seed-coats and study the albumen and embryo : The Bean, the 
Maple seed, the seed of Hemp, the seed of Morning-glory, the seed of the White 
Pine, the seed of Indian Corn, and that of the Horse-chestnut. Determine (1) 
which of these seeds are albuminous and which are exalbuminous ; (2) the posi- 
tion of the embryo as regards the albumen in case the seed possesses the latter ; 
(3) the parts of the embryo present in each case; (4) draw a diagram of each, 
representing the shape and parts of the embryos, and determine whether, in any 
instance, the caulicle is accumbent. 



PART II. 

HISTOLOGY. 



CHAPTER I. 



The Cell. — The Protoplast. — Other Cell-Contents. — The 

Cell-Wall. 



The Cell. All plants, whatever their size or kind, are composed 
of structural units known as cells. While some exceedingly small 
plants, chiefly microscopic in size, are composed of but a single 
cell, it is nevertheless a fact that the "higher" plants, those with 
which in our daily life and associations we have become more or 
less familiar, are composed of multitudes of cells varying widely 




Fig. 330. — Cells of Bottle Cork, illustrating empty, box-like compartments 
to which the name "cell" was originally applied. 

in size, form and structure and wonderfully adapted to the work 
which they are called upon to perform in the economy of the plant. 
The discovery of the cellular structure of plants is credited to 
Hooke, who in the year 1665, using a microscope which he had 
made or improved, saw and described the cells in Bottle Cork. The 
observations of Hooke were confirmed and extended by Malpighi 



132 



PART II.— HISTOLOGY. 



and Grew, before the close of the 17th century. These early inves- 
tigators devoted their study to the walls of the cells and but little 
attention was given to the cell-contents until, in 1846, von Mohl 
discovered the living substance and gave it the name protoplasm. 







^:V-^tt£*# 



Fig. 331. — Cells from the embryo of Corn, showing typical protoplasts, each 
containing a nucleus. 

Soon afterward came the comprehensive studies of Schleiden which 
laid the foundations for the modern science of cytology. 

The term cell, as applied to the minute box-like compartments 
(Fig. 330), is fairly descriptive, but in a wider sense cells are 
much more than empty cavities. Hence the need of a term to 
distinguish the living or protoplasmic contents of the cell, the wall 
being of secondary importance in the life of the organism. These 
living contents have now come to be known collectively as the Pro- 
toplast (Fig. 331). 



THE PROTOPLAST. 



Protoplasts are, therefore, the living cells of plant structures 
and alone possess those powers which we characterize as "vital" 
or intimately associated with life. Most evident among these 
attributes are: Metabolism, including the building up of food 



CHAPTER I. — THE CELL. 



133 



products from their elementary substances on the one hand, and, 
on the other, the utilizing of the energy stored in these foods by 
breaking them down into simpler compounds with the accompany- 
ing release of energy; growth, the power to increase in size by 
adding new but similar materials; division, accompanying repro- 
duction or regeneration; motion, whether expansion, contraction or 
streaming, and irritability, the power to respond to stimuli of 
various kinds, notably light, heat and gravitation. These quali- 
ties, of which more will be said in a later chapter, are inherent 
to the protoplast; all the various and wonderful manifestations 
of life, even in the largest and most complex plant structure, are 
but the sum of the activities of its component cells. 

If we examine, under the microscope, a section cut from a 




Fig. 332.— Represents diagrammatically a cell, greatly magnified, to show the 
parts, a, the cell-wall ; b, the middle lamella ; c, the ectoplasm ; d, cytoplasm ; 
e, vacuole ; f, nucleus ; g, chlorophyll granule ; h, intercellular space ; i, cyto- 
plasmic thread. 



young and growing part of a plant, we will find that each proto- 
plast is surrounded by a delicate, transparent and somewhat elastic 
membrane of cellulose which we call the cell wall. Though each 



134 PART II. — HISTOLOGY. 

protoplast originates and develops its own wall, yet, where cells 
meet, their walls usually become attached, forming a common wall 
between adjoining cells, but capable of being separated again 
through the action of certain solvents or re-agents. In every living 
cell there may be perceived a protoplast in which, upon closer 
inspection, several parts or regions may be distinguished: First, 
the cytoplasm, usually a soft, viscid, slightly cloudy and nearly 
colorless mass, resembling somewhat the white of an egg in 
appearance and in consistence. This nearly or quite fills the cell. 
Its structure is described as foamy and is compared with an 
emulsion consisting of tiny globules suspended in a fluid, though 
some investigators contend that this structure should rather be 
likened to a very delicate, spongy framework distended with 
liquid contents and containing numerous minute granules known 
as microsomes. Perhaps both views are approximately correct, 
under different conditions, for we know that cytoplasm is capable 
of great variations in consistence, depending upon the amount of 
water it has absorbed, also that it apparently is able to form 
within its mass various fibrils, granules and similar structures. 

As the cell grows, rifts appear in the cytoplasm. Such gaps 
are termed vacuoles, though they are not empty but are filled 
with cell-sap, reserve food and even waste products. (Fig. 332.) 

As the cell approaches maturity, the vacuoles increase in size 
and run • together, eventually leaving only a film of cytoplasm 
lining the walls. Even this lining disappears at last, the wall 
meanwhile having become more or less thickened, often with a 
transformation of the cellulose into some other wall substance. 

The protoplasts of adjoining cells are connected together by 
very thin strands of cytoplasm extending through minute pores 
in the cell wall and thus affording a means of communication 
between all the living cells of the plant and, in effect, uniting the 
protoplasts of the entire plant into one continuous whole. 

Concerning the chemical nature of cytoplasm, little has been 
definitely determined. That it is very complex, exceeding labile or 
unstable and changing its composition readily and with accom- 
panying release or absorption of energy, we are assured. These 
characters are distinctively "vital"; they are necessary to the 
manifestation of life; but, as regards the definite chemical compo- 
sition of cytoplasm and similar protoplasmic bodies, about all we 
can say is that these contain several or many protein substances, 
colloidal and nitrogenous, together with water in varying propor- 



CHAPTER I.— THE CELL. 



135 



tions, inorganic salts and various food materials. A distinction 
is here made between protoplasm, which is a definite substance, and 
cytoplasm, which is composed of protoplasm and various inclusions 
to be mentioned presently. 

Surrounding the cytoplasm closely and also in intimate contact 
with the cell wall is a delicate protoplasmic film termed the ecto- 
plasm, which is best seen when the protoplast is caused to contract 




Fig. 333. — Cells from the root tip of the Onion, showing the protoplasts ; 
a, cytoplasm; b, nucleus; c, nucleolus; d, chromosome; e, vacuole; f, cell wall. 



by applying salt solution. The ectoplasm controls the passage of 
materials to and from the protoplast and takes part in building 
the cell wall. A similar protoplasmic film lines the vacuoles. 

The nucleus is imbedded in the cytoplasm, usually toward the 
center of the cell, and in young cells occupying a half to three- 
fourths of the diameter. The nucleus is roundish or lenticular in 
shape and is constituted of a network or "reticulum" composed 
of threads of linin in which granular particules of chromatin are 
imbedded. These meshes hold a clear, fluid nuclear sap. There 
is also one or more tiny, globular, somewhat denser bodies termed 
nucleoli. A nuclear membrane, resembling the ectoplasm, sur- 



136 



PART II. — HISTOLOGY. 



-rounds the nucleus and separates it from the cytoplasm. (Fig. 
333.) 

The nucleus is, in a sense, the center of life of the cell, in 
proof of which we find that, at least in all but the lower unicellular 
plants, every living cell contains a nucleus. Further, the nucleus 
divides with accuracy into two equal and similar parts during 
cell-division. The elaborate precautions for ensuring the accuracy 
of this division make it seem probable that the nucleus bears the 
inheritable qualities. In fact, it has been suggested that the 




Fig. 334. Fig. 335. Fig. 336. Fig. 337. Fig. 338. 

Fig. 334. — A cell of Philotria, showing choroplasts of the ordinary lens- 
shaped form. 

Fig. 335. — A cell of Spirogyra, showing spiral chlorophyll bands. 

Fig. 336. — Two cells from Zygnema, showing stellate arrangement of chloro- 
phyll. 

Fig. 337. — A cell of Oedogonium, showing chains of chloroplasts. 

Fig. 338. — A cell of Mesocarpus, showing the chloroplast as a single green 
plate. 

nucleus controls and regulates the life of the protoplast in a manner 
remotely resembling the relation of the brain to the body of man. 
The nucleoli are apparently merely granules of food substance 
reserved for the nourishment of the chromatin. 

Among the other bodies enclosed in the protoplast, the chro- 
motophores are the most prominent: Under this name are in- 
cluded three groups of plastids which apparently originate in 
the neighborhood of the nucleus and are at first colorless, but 
more highly refractive than the surrounding cytoplasm. In such 



CHAPTER I. — THE CELL. 137 

plant parts as are exposed to sunlight, these plastids develop a 
green color and are then known as chloroplasts or chlorophyll 
granules. They are commonly lens-shaped or elliptical and flat- 
tened and are found chiefly in the outer portion of the cytoplasm, 
adjoining the cell wall (see Fig. 334). In the lower plants the 
chlorophyll may take the form of spiral bands, as in Spirogyra 
(see Fig. 335), stellate masses, as in Zygnema (see Fig. 336), or a 
variety of other shapes (see Figs. 337 and 338). Each chloroplast 
is composed of a colorless, protoplasmic base, infiltrated with a 
solution of a green pigment, chlorophyll, which, in turn, is com- 
posed of several pigments: chlorophyll a and chlorophyll b, con- 
stituting the green part, and carotin and xanthophyll, the yellow 
part. This green pigment may be extracted by alcohol, ether or 
chloroform, leaving the granules colorless. The solution is dichro- 
matic, being a bright green in a thin layer and blood-red in a 
thick layer when viewed by strong light passing through it. Under 
the spectroscope it presents a characteristic absorption band in 
the red part of the spectrum. 

The green color of plants is due to chlorophyll, which, however, 
is frequently masked by other colors dissolved in the sap, as in 
many Algse, as well as in our so-called "foliage plants." Under 
certain circumstances chlorophyll undergoes disorganization; an 
instance is the production of the beautiful variations of color 
familiar to us in autumn foliage. If kept away from light, green 
plants may gradually become yellow or "etiolated"; the blanching 
of celery is an example. In such parts of plants as are not 
exposed to light, the chromatophores fail to develop green color 
and remain as leucoplasts. These are usually globular in shape 
and may contain crystals of proteid substance. 

Chromoplasts differ from the preceding in their color, which 
ranges from yellow to red, and in their often crystal-like shape, 
due to the crystallization of their coloring matter. They arise 
either directly from chromatophores or from chloroplasts, and, 
like the latter, have a colorless base or stroma. The yellow and 
orange colors of many flowers and fruits are due to the chromo- 
plasts they contain. 

In the peculiar plants known as Fungi, chromatophores of all 
descriptions are absent. 

OTHER CELL CONTENTS. 

Other Cell Contents, sometimes considered as .inclusions in the 
protoplast, comprise the products of photosynthesis, such as starch, 



138 



PART II. — HISTOLOGY. 



sugar and other carbohydrates; fixed oils and fats, especially 
abundant in seeds; the protein substances, notably aleurone; the 
inorganic salts, most prominent among which are the various 
forms of calcium oxalate crystals; the tannins, of frequent occur- 
rence especially in the outer tissues of plants; the volatile oils 
and resins; the mucilages, the glucosides, the alkaloids and the 
enzymes. 




Fig. 339. — A cell from the calyx of the Nasturtium, showing, a, crystal-like 
chromoplasts, and b, nucleus. 

Starch is the first visible product of photosynthesis and is 
found in chloroplasts whenever these have been exposed to light. 
This "assimilation starch" represents the transformation of the 
radiant energy of sunlight into the potential energy stored up 
in the carbohydrate. Starch is built up from the carbon dioxide 
of the air and the water from the soil, and appears first as 
glistening particles imbedded in the chloroplasts. It is generally 
assumed that glucose is formed primarily, but is rapidly condensed 
into starch. Almost as fast as they are formed, the granules of 
assimilation starch are attacked by the enzymes of the protoplast 
and dissolved, so that their mass does not greatly increase, and 
upon the approach of darkness, when the production of starch 
ceases, the tiny starch bodies soon disappear entirely from the 
chloroplasts. In a soluble form the starch is transported to the 
storage tissues of the plant, where with the aid of the leucoplasts 
or "starch-formers" it is deposited as grains of "reserve starch." 

All our food and drug starches are reserve starches. Their 
grains are of definite shape and structure, being built up of layers 
formed about a centre called the hilum and which may occupy the 



CHAPTER I. — THE CELL. 139 

geometric centre of the grain (concentric) or may, more commonly, 
be situated toward one side (excentric). These layers are due in 
part to the variation in the water content of the different parts 
of the grain. The stratifications thus formed are more distinctly 
seen when the grains are mounted in water and usually show to 
the best advantage at the moment that the grain swells, when 
acted upon by alkali or boiling water. Starch solutions, obtained 
by the action of boiling water, alkalies, acids or digestive ferments, 
are thick and colloidal, and give at first the characteristic blue 
color with iodine. This blue color is destroyed by heat but reap- 
pears on cooling. Some starches give a purple rather than a 
blue color with the reagent. Under the microscope, undissolved 
starch grains in contact with an excess of iodine finally become 
black. 

The starches belong to the class of carbohydrates known as 
polysaccharoses, the empirical formula usually assigned to these 
being (C 6 Hi O 5 )n, in which n may be any number from 20 to 200. 
When viewed under the microscope by polarized light, starch 
grains exhibit a dark cross, the arms of which intersect at the 
hilum of the grain. Not only do starch grains differ in size, 
ranging from one to as much as one hundred seventy microns 
(0.001 to 0.17 Mm.), and in shape, being spherical, polyhedral, 
oval, disk-like, elliptical and with various knobs and projections, 
but they differ also in the form and distinctness of their stratifica- 
tions as well as in the cleft, which appears in some grains as 
simple short lines or fissures extending through the hilum but in 
others is variously branched and stellate. Simple starch grains 
possess but one hilum, but compound starch grains have two or 
more hilums with a set of stratifications around each. Large 
compound starch grains are found in oats and in rice; smaller 
compound grains occur in many drugs. While these characters of 
starch grains vary widely in different plants, yet they are fairly 
constant for each species and hence are of considerable diagnostic 
value in the study of foods and drugs. (See Figs. 340 to 347.) 

Inulin is a carbohydrate which is closely related to starch and 
isometric with it. It takes the place of that substance in many 
members of the Composite. It is abundant, for example, in the 
roots of Elecampane, Dandelion, Chicory, Dahlia and the Arti- 
choke. It is also occasionally found in members of other families. 
Inulin occurs in solution in the cell-sap, but if parts containing it 
be soaked for a time in strong alcohol, and sections of them be 



140 



PART II. — HISTOLOGY. 



examined microscopically, sphsero-crystals of it will be observed 
in the cells, as shown in Fig. 348. Iodine does not stain inulin 




Fig. 348. — Sphaero crystals of inulin; A and F, deposited by crystallization 
from an aqueous solution. B, from Dahlia tuber. C, E, and F, from Helian- 
thus tuberosus. D, fragment of a sphaero crystal. B, C, D .and E, after treat- 
ment with alcohol. (Sachs.) 

blue, as it does starch, but, like starch, it is converted into glucose 
by the action of dilute sulphuric acid. 

Sugars. The sugars are sweet and crystallizable principles of 
plants and occur in solution in the cell-sap. Attention has already 



(SEE ILLUSTRATION ON OPPOSITE PAGE.) 

340.' — Manihot starch, showing truncate forms. 

341. — Corn starch, showing angular and rounded forms. 

342. — Starch from the latex of Euphorbia splendens, showing bone- 

nd club-shaped forms. 

343. — Starch from Colchicum corm, showing compound grains. 

344. — Bean starch, showing characteristic clefts. 

345. — Wheat starch, showing lenticular grains. 

346. — Potato starch, showing excentric stratifications. 

347. — Oat starch, showing compound grains with numerous individual 



Fig. 

Fig. 

Fig. 
shaped a 

Fig. 

Fig. 

Fig. 

Fig. 

Fig. 
granules. 



CHAPTER I. — THE CELL. 



141 



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C 



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Fig .34- 1 & 



n ■ u 



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142 PART II. — HISTOLOGY. 

been called to one of the sugars, glucose, which, presumably, is the 
form in which carbohydrate is first produced in photosynthesis. 
From this basal photosynthate the more complex carbohydrates, 
notably starch, are apparently built up. 

In general, sugars char when strongly heated, are freely soluble 
in water but only slightly soluble in alcohol. The sugars are 
divided into two groups, the monosaccharoses, -formerly known as 
glucoses, and the disaccharoses, formerly known as saccharoses. 

The monosaccharoses comprise the simple sugars, that is, those 
that do not hydrolyze into other sugars. They contain from two 
to nine carbon atoms in the molecule and classified accordingly as 
bioses, trioses, tetroses, pentoses, hexoses, etc 

The hexoses are the most important group of monosaccharoses. 
They have the formula C 6 Hi 2 6 and include two common plant 
sugars, glucose, known also as dextrose, grape sugar or starch 
sugar, and fructose, known also as levulose or fruit sugar. Both 
of these share with the other monosaccharoses certain properties 
common to the group and may be recognized by their power of 
reducing an alkaline solution of copper sulphate (Fehling's solu- 
tion) with the production of a deposit of red cuprous oxide. 

As indicated by their names, dextrose rotates the plane of 
polarized light to the right and levulose to the left. Both are 
fermentable by yeast. They occur associated together in many 
fruits. Fructose is considerably sweeter than glucose. 

The disaccharoses have the formula C^EUOn and yield upon 
hydrolysis two molecules of a hexose, not necessarily identical; 
thus cane sugar hydrolyzes into invert sugar, composed of dextrose 
and levulose. Cane sugar, known also as saccharose or sucrose 
(names which are also applied to the class) is the most important 
member of this group and may be distinguished from the hexoses 
as well as from most other disaccharoses by the fact that it does 
not reduce Fehling's solution. It occurs in Sugar cane as well 
as in Beet root, Sorghum, Sugar Maple,- some palms and other 
plants, in fact is quite widely distributed. It crystallizes in the 
form of monoclinic prisms or pyramids. Other disaccharoses are 
maltose, occurring in germinating cereals, and trehalose, which is 
found in certain fungi. 

Other Carbohydrates. As has already been pointed out, starch 
and inulin are closely related to the sugars, being, in fact, poly- 
saccharoses. To the carbohydrates belong also pectose, the gums, 
hemi-cellulose and cellulose. 



CHAPTER I. — THE CELL. 143 

Mucilage or gum occurs as cell-contents in relatively few 
instances. When so occuring, it is stored as a reserve food. Exam- 
ples are afforded by the medicinal Salep, which is the tuber of an 
orchid, and by the succulent leaves of the Aloe and the bulb-scales 
of the Onion. 

Far more frequently, mucilage is the result of a metamorphosis 
of the cell-wall and such "membrane mucilage" will be again men- 
tioned in discussing the wall. 

In general, gums or mucilages are characterized by their prop- 
erties of swelling and at least partly dissolving in water. They 
are usually grouped according to their composition. Those con- 
taining arabic acid and its compounds, of which class Gum Arabic 
is a type, are completely soluble in water. Those containing 
bassorin, such as Gum Tragacanth, are only partly soluble. Those 
containing cerasic acid, such as Cherry gum, form a third class. 
Cellulose, hemi-cellulose and pectose are cell-wall materials and 
will be considered later. 

Fixed Oils and Fats. These occur in the cells of various parts 
of plants, but are particularly abundant in certain fruits, as those 
of the Olive, and in many seeds. They are formed in the proto- 
plast ultimately from glucose. They exist either as tiny drops 
suspended in the cytoplasm or in somewhat larger globules con- 
fined within the vacuoles, and are usually associated with other 
food substances. They replace starch as a reserve food material, 
and hence are of great importance to the plant. Chemically con- 
sidered, they are glycerides of various fatty acids such as oleic, 
stearic, palmitic or related acids. It is noteworthy that in fats 
the proportion of oxygen to that of carbon and hydrogen is very 
small. 

Lecithins are also of frequent occurrence and are related to 
fats as well as to proteins. 

The waxes, which, in their chemical nature, are allied to fats, 
being compounds of fatty acids with alcohols derived from the 
higher fatty hydrocarbons, sustain very different relations to the 
life of the plant. Instead of serving as reserve food-materials, 
they appear to be purely protective in their function. They occur 
as excretions on the cuticularized epidermis of many plants. The 
"bloom" of certain fruits is of this nature, and the glaucous 
appearance of the leaves and stems of many plants is due to the 
same cause. The parts covered by it are thus protected from wet 
and from the spores of destructive fungi; it doubtless serves also 



144 PART II. — HISTOLOGY. 

to check excessive evaporation from the plant. Occasionally, as 
in the case of the Brazilian and Andean Wax Palms and the Wax 
Myrtle of our New England coast, the secretion is sufficiently 
abundant to be of commercial importance. 

Proteins. These are complex nitrogenous substances more or 
less colloidal in nature and, in plants, mostly stored as reserve 
food. It would appear that, in the metabolism of the plant, pro- 
teins are built up from amides and amino-acids and, when proteins 
are acted upon by enzymes, the simpler and more soluble nitrog- 
enous substances are again produced. All of these originate in 
the cytoplasm and, unlike the carbohydrates, do not depend upon 
photo-synthesis for their formation, hence they occur in fungi as 
well as in green plants. 

The proteins are characterized by their large and complex 
molecules but differ much in solubility and digestibility. 

Hundreds of proteins have been named and grouped under cer- 
tain general classes; among them are the globulins, which are 
insoluble in pure water but soluble in neutral saline solutions and 
coagulated by heat; the albumins, which are soluble in water but 
coagulated by heat; the glutelins, insoluble in neutral aqueous solu- 
tions and in alcohol but readily soluble in dilute acids and alkalies, 
and the prolamins, which are soluble in alcohol but insoluble in 
pure water. 

In the dry, storage tissues of seeds, reserve proteins are found 
in characteristic forms known as crystalloids and aleurone 
grains. Crystalloids are composed of globulins crystallized into 
cubical or rhombohedral forms and readily distinguished from 
ordinary crystals by their property of swelling in contact with 
water. Crystalloids are frequently found imbedded in aleurone 
grains and occasionally occur suspended in the cytoplasm even in 
other than storage cells. 

Aleurone grains are rounded bodies, formed in the vacuoles of 
the protoplast and consisting chiefly of globulins. When associated 
with starch in seeds, they are usually very small and fill in the 
spaces between the starch grains. In fatty seeds such as the 
Castor Bean, the aleurone grains are larger and consist of a mass 
of ground- substance, composed of water-soluble globulins and 
surrounded by a firmer membrane of similar material. Within 
such aleurone grains are various inclusions, chiefly crystalloids, 
globoids and tiny rosette crystals of calcium oxalate. The globoids 



CHAPTER I. THE CELL. 



145 



are rounded, as the name implies, and are composed of calcium and 
magnesium phosphates in combination with organic substances. 
(See Figs. 349 to 355, inclusive.) 

The albumins exist in many plant juices. Some of them, such 
as the ricin of Castor Bean, are powerful poisons and are distin- 
guished as tox albumins. 



7 \/f v A 



355 



w 



\w x/ 



fefep >&. 



- 



J& 




351 









Fig. 349. — Aleurone grains from the Castor bean ; a, a grain viewed in direct 
transmitted light, showing a single crystalloid and globoid. b, the same grain 
in indirect light, showing its ellipsoidal shape. c. the same grain viewed on 
end. the globoid toward the top. d. a grain viewed in direct light, showing a 
crystalloid and three globoids, e. the same grain in a different position, showing 
several globoids, f, two grains each with a globoid but no crystalloid, g, a grain 
with crenate or pitted surface and no crystalloid visible, h, a grain with large 
crystalloid and numerous small globoids. 

Fig. 350. — Aleurone grains from the Brazil nut. Each grain usually con- 
tains one crystalloid and one globoid or a globoidal mass. The envelope is very 
thin. 

Fig. 351. — Aleurone grains from Fennel fruit. Globoids are seldom visible, 
but rosettes of calcium oxalate crystals are present in all but the larger grains. 

Fig. 352. — Aleurone grains from Almond. The smaller grains each contain 
one or more very small globoids, while the larger grains sometimes contain a 
rosette of calcium oxalate crystals. 

Fig. 353.— Aleurone grains from Nutmeg. The crystalloids are very per- 
fectly formed. The globoid is attached at one corner of the crystalloid by a very 
thin envelope. 

Fig. 354. — A cell from the aleurone layer of Wheat. The aleurone is in 
very small angular grains, frequently called "amorphous" aleurone, and sur- 
rounds the denser nucleus. 

Fig. 355. — A cell from Pea seed inclosing: a, the nucleus; b, ectoplasm; c, 
starch grains ; d, small aleurone grains. 



146 PART II. — HISTOLOGY. 

The gluten of Wheat, which determines the dough-making 
qualities of flour, is a mixture of a glutelin (glutenin) and a 
prolamin (gliadin). 

The conjugated proteins, highly complex in chemical structure 
and less readily digestible than the simple proteins, include the 
nucleins, which contain phosphorus (phospho-proteins) and occa- 
sionally iron or sulphur. They are not attacked by pepsin but are 
dissolved by alkaline solutions. 

The protein derivatives result from the hydrolysis or cleavage of 
the simple proteins when digested by enzymes or dissolved by 
dilute acids. Peptones and proteoses are soluble and diffusible 
proteins thus produced, and these are in turn resolvable into 
amino-acids. 

Enzymes are complex organic substances, possibly proteins, of 
whose composition little is known. They are characterized by their 
power of bringing about important chemical changes in substances 
with which they are in contact, without themselves entering into 
permanent combination or suffering material loss. They are, 
therefore, organic catalysts, and are, perhaps, the most important 
of the cell contents. Enzymes are sometimes styled unor- 
ganized ferments, as distinguished from organized ferments such 
as yeasts and bacteria. The distinction scarcely holds, however, 
since it has been shown that the catalytic power of organized 
ferments depends upon enzymes which they contain. A better 
division is that into endocellular enzymes, which cannot diffuse out 
of the cell, and extracellular enzymes, which can do so. A pecu- 
liarity of enzymes is the great amount of material which can be 
changed or converted by a relatively very small amount of the 
ferment. Thus diastase, the enzyme obtained from malt, can 
hydrolyze ten thousand times its own weight of starch, and rennet, 
an animal ferment, is capable of coagulating a half million times 
its own weight of casein. Enzymes are sensitive to heat and light. 
All are destroyed at 100° C; few can be safely exposed to heat 
above 60° C. Like living organisms they have an optimum temper- 
ature at which they are most active. Above this point their 
activity becomes permanently impaired. They withstand low 
temperatures without injury. 

Certain substances stimulate the activity of enzymes. Such 
activators include a variety of chemical substances, acids, alkalies 
and salts, and may be separated from the ferment by dialysis. 



CHAPTER I. — THE CELL. 147 

The activity of an enzyme may be suspended by the removal of 
its activator and restored by again adding this to it. In some 
instances the enzyme is only developed by the action of the acti- 
vator on an inactive substance, the zymogen formed in the cell. A 
kinase is a complex organic body, colloidal in nature, which acti- 
vates the zymogens in living tissues. 

Inhibitors of enzyme action are called paralyzers. They may 
be foreign or be the result of enzyme action itself. Thus alcohol, 
formed by the action of yeast, will in sufficient strength destroy 
the ferment that produced it. Antiseptics are paralyzers, notably 
bichloride of mercury. 

Enzymes are usually grouped according to their reactions: 
The first group includes those enzymes which hydrolyze or cause 
the addition of water to certain substances, which are then mostly 
broken up into simpler substances. The digestive ferments fall in 
this group. Diastase, or amylase, converts starch into glucose; 
protease, identical with pepsin, changes insoluble proteins into 
soluble peptones; cytase converts cellulose into soluble forms; 
lipase digests fats and fixed oils, converting them into fatty 
acids and glycerin; emulsin and myrosin have the power of hydro- 
lyzing the glucosides amygdalin and sinigrin, respectively, with 
the production of the volatile oils of bitter almond and of black 
mustard. 

The second group of enzymes cause the splitting of certain 
substances without the accompanying hydration. The zymases, 
among which are the enzymes of yeast, represent this class. 

The third group are the oxydases or oxidizing enzymes, such 
as the ferment, produced in the acetic bacteria, which oxidizes 
alcohol to acetic acid. It is to enzymes of this group that the 
darkening in color of freshly cut fruits and of mushrooms is due. 

The fourth group is the reducing enzymes or katalases, which 
may reduce nitrates to nitrites, or hydrogen peroxide to water and 
oxygen. 

It must be borne in mind, however, that not only the analytic 
but the synthetic powers of living cells depend upon the enzymes 
formed therein, so that the entire metabolism of the plant, its 
growth and maturation, no less than its senility and decay, are 
contingent upon these little-known but very necessary agents. 

Important industrial processes, such as the making of bread 
and of cheese, brewing, the "retting" of flax and many others, 
depend upon enzymes for their operation. 



148 PART IT. HISTOLOGY. 

Glucosides. The glucosides are substances found in solution in 
the cell-sap, and whose peculiarity consists in the fact that under 
the influence of enzymes or ferments which occur in the cells with 
them, they are decomposed into glucose or some similar sugar and 
another substance capable of still further decomposition. The 
hydrolysis or splitting of glucosides may also be effected by dilute 
acids and alkalies. 

An example is afforded by Amygdalin, which under the influence 
of an enzyme, emulsin, hydrolyzes into glucose, benzaldehyde and 
hydrocyanic acid. This and other cyanogenetic glucosides are 
widely distributed in the plant world. They are familiar to us in 
bitter almond and in wild cherry bark. Another rather widely- 
distributed glucoside, Hesperidin, is often met with in crystalline 
form, especially in the rind of citrus fruits. The saponins, charac- 
terized by their property of frothing in water, are a group of 
glucosides, members of which are found in a large number of 
plants. An important medical saponin is Digitonin from Digi- 
talis leaves. 

The glucosides are mostly soluble in water; quite a number can 
be crystallized from their solutions. Many are active medic- 
inal principles; some of them, such as strophanthin, are highly 
poisonous. 

Pentosides, such as Aloin, the cathartic principle of aloes, are 
closely related to glucosides but yield pentose instead of glucose 
on decomposition. 

Glucosides are usually regarded as reserve food-materials, the 
sugar part of the molecule being dissociated by hydrolysis for 
use by the plant, the other part of the molecule remaining in the 
cell and combining again with sugar when an excess of carbo- 
hydrate is available. Probably other functions, such as protection 
against animals, antisepsis of injured tissues and excretion of 
sugar in the extra-floral nectaries, may also be served by these 
very diverse bodies. Glucosides may occur in any or all of the 
storage tissues of the plant or may be stored temporarily in the 
leaves, and later translocated to the permanent storage tissues 
of the cortex. 

Alkaloids. These are potent principles of plants, including some 
of the most valuable of medicines as well as some of the most 
powerful of poisons. As a class, they are nitrogenous organic 
bases and combine with acids to form salts, thus showing their 
resemblance to alkalies, whence the name alkaloid. They are 



CHAPTER I. — THE CELL 149 

formed in considerable variety and through a wide botanical range, 
though many plants do not possess them at all. It has not been 
ascertained that alkaloids are of any service to the plant, except, 
perhaps, as a means of defense against predacious animals and 
parasitic fungi. They may even be injurious to the plants that 
produce them. In reserve tissues of the plant, especially in rhi- 
zomes, corms, bulbs and roots, alkaloids are usually associated 
with stored food and larger in amount at the periods when this 
reserve food is at its maximum, but in the leaves and tops of 
plants, alkaloids are usually most abundant at the time of flower- 
ing or immediately thereafter. In most instances the alkaloids 
are found in the plant in combination with organic acids, especially 
tannic and malic acids, or with some characteristic acid, as meconic 
acid in Opium. 

Among the better-known alkaloids are Quinine, from the 
Cinchona barks; Morphine and Codeine, narcotic principles of 
Opium; Cocaine, the enslaving alkaloid from Coca leaves; Strych- 
nine, the poisonous alkaloid obtained from Nux Vomica; the even 
more poisonous Atropine, from Belladonna; Caffeine, found in 
Tea, Coffee, Cola, Guarana and Mate, and to which the stimulant 
effect of beverages prepared from these is due; Theobromine, 
closely related to Caffeine and found in Cacao seeds and hence in 
Chocolate; Nicotine, the volatile alkaloid of Tobacco, and Musca- 
rine, the deadly poison of some of the Mushrooms. 

According to their chemical relationship, alkaloids are classified 
into several groups, among which are: 

The Purine group, including Caffeine and Theobromine, both 
having but feebly basic properties and apparently decomposition 
products of proteins, corresponding to urea and uric acid in 
animals. 

The Quinoline group, comprising the alkaloids from Cinchona 
and Nux Vomica and restricted to the Rubiaceae and Loganiaceae 
respectively. 

The Isoquinoline group, including Morphine and Papaverine, 
from the medicinal Poppy, and Berberine, restricted to the order 
Ranales. 

The Pyridine group, including the liquid and volatile alkaloids, 
these being mostly derivatives of Pyridine. Among them are Are- 
colin, Piperine, Coniine and Nicotine. 

The Pyrrolidine or Tr opine group, including the solanaceous 



150 PART II. — HISTOLOGY. 

or mydriatic alkaloids, Atrophine, Hyoscine and Hyoscyamine, as 
well as Cocaine and Pelletierine. 

As a class, the uncombined alkaloids are largely soluble in 
strong alcohol, chloroform or ether, while their salts are most 
readily dissolved by water or diluted alcohol and are not soluble 
in chloroform or ether. Among the reagents for alkaloids are 
phospho-molybdic acid, which precipitates nearly all alkaloids, and 
potassium-mercuric iodide (Mayer's reagent), which precipitates 
many of them. Tannic acid as well as iodine also reacts with most 
alkaloids. Gold and platinum chlorides form characteristic micro- 
crystals with certain alkaloids. 

Tannins are astringent substances which, dissolved in the cell 
sap or deposited in cells in amorphous form, are widely distributed 
in plants and recognized by their property of striking blue-black 
or green colors with solutions of iron salts. Tannins are often 
present in considerable quantities in epidermal cells, especially 
in winter leaves. Yellowish or reddish-brown substances, at least 
partly tannin, often fill the cavities of thick-walled cork cells. 
Excretory tannin products are sometimes found in special cells 
occurring in rows and following the course of the conducting bun- 
dles or in sac-like or tubular cells, various in form and structure, 
developed in the parenchyma tissue. 

The value of tannins to the plant is doubtful. Like glucosides 
and alkaloids, they may serve in some instances as a means of 
protection against animal attacks or to repel parasitic fungi, 
especially when the tannins are situated in the epidermis or the 
cork. 

Chemically, the tannins are divided into tannides, which have 
the nature of glucosides, and tannoids, which do not yield glucose 
when hydrolyzed by acids. These groups are further divided into 
catechu-tannins and gallo-tannins, related to protocatechuic and 
gallic acids, respectively. 

Tannins are soluble in water, alcohol or a mixture of alcohol 
and ether. Their solutions give distinct color reactions with ferric 
chloride, ferrous sulphate, copper acetate, and other reagents. 
They precipitate albumin, gelatine and most of the alkaloids. In 
alkaline solutions, tannins absorb oxygen and darken in color. 

Volatile Oils. Essential or volatile oils are usually the odorous 
principles of the plants that contain them. Although bearing 
some resemblance to the fixed oils or fats, they differ from these 
widely in chemical nature and are themselves, in fact, a most 



CHAPTER I. — THE CELL. 151 

heterogeneous group, including mixtures of various principles; 
terpenes, esters, alcohols, phenols, aldehydes, ketones and lactones, 
as well as compounds of sulphur and of nitrogen. 

While some of these originate in the protoplast as such, others 
result from the decomposition of glucosides and even through the 
conversion of the cell-wall substance. 

They are often excreted along with resins into secretion reser- 
voirs (see page 211). 

Some volatile oils are of service to the plant in protecting it 
against injurious insects or other animals, and perhaps also 
against destructive fungi, while others, as the floral perfumes, 
are useful, as we have already seen, in attracting insects to flow- 
ers, and so effecting cross-fertilization by their agency. 

Volatile oils are widely distributed among the flowering plants 
and are especially abundant in certain groups, notably the families 
Conifer x, Labiatse, Umbelliferse, Myrtaceas, Rutaceas and Zingibe- 
racese. 

Resins, Oleo-resins, Gum-resins, and Balsams. Resins are very 
common constituents of plants. They appear to be of the nature 
of excretory products, either occurring normally, or produced 
pathologically as the result of injuries to the plant. They are 
either produced in special cells, or groups of cells, called glands, 
occurring on the surface of plants, or forming the terminal cells 
of glandular hairs, or else in internal cells which pour their secre- 
tions into intercellular spaces, called secretion reservoirs (see 
page 211). They are, for the most part, amorphous, more or 
less transparent, readily fusible substances, which cannot be vola- 
tilized without change, and which are soluble in alcohol, and in the 
volatile oils, but not in water. Tschirch classifies resins into the 
following groups: tannol resins, resene resins, resinolic acid resins, 
resinol resins, pigment resins and glucosidal resins. When resins 
are associated with volatile oils, as in Copaiba and common Tur- 
pentine, they are called oleo-resins; if they contain benzoic or 
cinnamic acids, either with or without volatile oils, they are called 
balsams or balsamic resins, respectively, and if mixed with gums, 
they are termed gum-resins. The last are often constituents of 
the milk-juice of plants. Styrax, Peru balsam and Tolu balsam 
are examples of the balsams, and Gamboge, Myrrh and Asafcetida 
of gum-resins. Caoutchouc and Gutta-percha are peculiar resinous 
constituents of the milk-juice of some plants. 

Acids. Among the more important of these may be mentioned 



152 



PART II. — HISTOLOGY. 



malic acid, a very common acid in fruits, but also found in other 
parts of plants; oxalic acid, abundant and widely distributed; 
citric acid, which communicates the acidulous taste to lemons, 
limes, and other citrus fruits, and which not infrequently occurs. 





Fig. 356. — (Above.) Section .of Witch-hazel hark, showing hexagonal crys- 
tals of. calcium oxalate in the cells. A. several crystals isolated from the cells. 

Fig. 357. — (Below.) Section of Rhubarb, showing rosette cluster^ of crys- 
tals of calcium oxalate. A, diagrammatic forms of these rosettes. 



CHAPTER 



-THE CELL. 



153 



also, in other fruits; and tartaric acid, which exists in considerable 
quantity in grapes, but is not wanting in many other fruits. How- 
ever, many other acids occur less abundantly. Acids may exist free 
or in combination with various bases. The acid reaction which 
many plants exhibit may be due either to the presence of free 
acids, or to acid salts in solution. 

Mineral Substances. The cell sap contains many inorganic sub- 
stances in solution, such as silica, and salts of potassium,, sodium, 
calcium, magnesium and iron. Silica and salts of calcium may be 




ir/«* 



Fig. 358. — Monoclinic crystals, showing hemitrophy, commonly called "twin 
crystals," from soap-tree bark. 

deposited, either in the amorphous or crystalline form, in the 
substance of the cell-wall. But, besides these, crystals of mineral 
matter are often found in the interior of cells. 



154 



PART II. — HISTOLOGY. 



By far most common among these is calcium oxalate; calcium 
carbonate occurs much less frequently and other inorganic sub- 
stances but rarely. 




Fig. 359. — A cell from Belladonna root, showing cryptocrystals or "crystal- 
sand." A, a more highly magnified view of several of these crystals. 

Fig. 360. — Section of Nutgall, showing prismatic crystals in the cells. A, 
diagrammatic form of these crystals. 



CHAPTER 



-THE CELL. 



155 



Crystals of calcium oxalate occur chiefly in monoclinic forms 
and the following types are met with: 

(a) Single crystals in pyramids, prisms or somewhat irregu- 
lar hexagonal shapes (Figs. 356 and 360). Occasionally double 
or twin crystals occur, notably in Soapbark (Fig. 358). 

(b) Needle-shaped crystals or raphides, either solitary or in 
sheaf -like groups, the latter usually surrounded by mucilage and 




Fig. 361. — Inner bark of Cascara Sagrada : 1, formation of a row of rosette 
clusters in a single parenchyma cell ; 2, living parenchyma cells ; 3, formation 
of a row of prismatic crystals in a single fiber cell ; 4, rosette clusters in a row 
of cells developed from a single cell; 5, developing bast fibers; 6, crystal fibers 
containing prismatic crystals, separated by septs ; 7, ends of mature bast fibers. 

contained in long, thin-walled parenchyma cells (Figs. 362, 363, 
364, 365, 366 and 367). 

(c) Rosette clusters or aggregates, consisting of numerous 
small pyramids, prisms or hemihedral crystals arranged around a 
central point or axis, so as to somewhat resemble a rosette or star 
in appearance (Fig. 357). 

(d) Crypto-crystals or "crystal sand," formed of deposits of 
very minute crystals of arrow-head shape, which occasionally fill 
parenchyma cells, giving to such cells a dark gray appearance that 
is characteristic (Fig. 359). 



156 



PART II. — HISTOLOGY. 



(e) Crystal fibers, consisting of monoclinic prisms or rosette 
clusters occurring in a row in a fiber-like cell extending lengthwise 
along the groups of sclerenchyma fibers and divided by septa into 
compartments, each usually holding one crystal (Fig. 361). 

Calcium oxalate is recognized by its being insoluble in water, 



^* 



3G2, 



3fv 111 






3^ 





Fig. 362. — Radial longitudinal section of the dried bulb scale of Squill, 
mounted in alcohol : 1, bundle of raphides enclosed in a hardened and shrunken 
mass of mucilage ; 2, nucleus and cytoplasm of the large cell, containing raphides ; 
3, parenchyma cells, containing nucleus and cytoplasm. 

Fig. 363. — Transverse section of same : 1, 2 and 2, as under Fig. 362 ; 4, a 
bundle of short raphides in longitudinal view. 

Fig. 364. — Raphides from Squill separated from the tissues. 

Fig. 365. — Transverse section from dried bulb scale of Squill, mounted in 
water: 1, bundle of raphides with mucilage coat dissolved awav ; 3, epidermis. 

Fig. 366. — Longitudinal section of same: (numbers 1 and 3 as under pre- 
ceding figure ; 2, wood bundle. 

Fig. 367. — Bundle of raphides enclosed in hardened mucilage and separated 
from cell. The broken raphides project slightly above the cut surface of the 
mucilage. 

alkali or acetic acid, but soluble without effervescence in hydro- 
chloric acid. 

Calcium carbonate is present in certain plants belonging to the 
Urticaceae (Fig. 368) and Acanthaceae in concretions or amor- 
phous masses deposited on a cellulose core and forming the pecu- 
liar structures known as cystoliths. Curious stalked cystoliths 



CHAPTER 1. — THE CELL 



157 



occur in large cells just beneath the upper epidermis in the leaf 
of Ficus elastica (Fig. 369). Upon treatment with hydrochloric 



32P 

T17T 



flHU 




,Docxpoijggjr « 
frrrrTTrrri^ 




Fig. 368. — Cystoliths in the hairs of the leaf of Hemp ; a, upper ; b, lower 
epidermis. 

acid the calcium carbonate dissolves, giving off bubbles of carbon 
dioxide and leaving a skeleton of cellulose. 



THE CELL WALL. 

While naked protoplasts are found in the earliest stages of 
development in plants, notably the cells of the embryo-sac (see 
page 106, Part I), as well as the gametes -generally, and while 
certain kinds of spores of the cryptograms are also of this 
description, yet these instances must be considered as exceptional, 
for, as a rule, every plant cell is surrounded by a cell-wall, devel- 
oped by the protoplast and consisting at first of a delicate film 
composed essentially of cellulose (see Fig. 333). As growth 
proceeds, the wall not only becomes thickened to a greater or less 
extent, but usually unequally so, and this gives rise to markings 
more or less conspicuous, which may either be irregular in form 



158 



PART II. — HISTOLOGY. 




Fig. 369. — Stalked cystolith in the leaf of Ficus elastica : a, epidermis with 
thickened cuticle; b, water storage cells; c, palisade parenchyma; d, cystolith in 
sac. 




Fig. 370. — Spores of Lycopodium species, showing markings in the form of 
protuberances on the cell wall, a, c and e, the whole spores ; b and d, sec- 
tioned spores, showing the interior without cell contents. 



CHAPTER I. — THE CELL. 



159 



and distribution, or else quite regular and characteristic of certain 
classes of cells. The markings may take the form of thickenings 
or protuberances on the outside of the cell-wall, as in the spores 
of Lycopodium species (see Fig. 370). This cannot well occur, 
however, except in cells which become independent at or before 




Fig. 372. 
Fig. 378. 

Fig. 377. 

Fig. 371. — Thin-walled parenchyma cells from the tuber of potato, the double 
wall of cellulose about 0.002 m.m. thick. 

Fig. 372.— Thick-walled parenchyma cells from Cascara Sagrada bark, the 
double wall of cellulose about 0.001 m.m. thick and containing prominent pores. 

Fig. 373. — Collenchyma cells, cut transversely, from the bark of Abutilon 
avicennae, the corners of the cells filled with bands or rods of cellulose extend- 
ing lengthwise of these much elongated cells. 

Fig. 374. — Sclcrenchyma cells from Cascara Sagrada bark, the walls much 
thickened and lignified, with stratifications plainly visible, and with distinct 
pores leading from the cavity of the cell. 

Fig. 375. — Portion of tracheal tube cut longitudinally from the rhizome of 
Gelsemium sempervirens, showing a thickened lignified wall, but the thickening 
laid on in anastomosing bands or rods extending tangentially around the tube 
and forming a net-work. 

Fig. 376. — Portion, including the end, of a bast fiber from Cinnamon bark, 
the wall lignified and so thickened as to reduce the cavity of the cell to a tiny 
canal with branches forming pores. 

Fig. 377.- — Portion of a cylindrical tracheal tube from the Corn stem, the 
thin cellulose wall strengthened by thickenings in the form of occasional rings, 
which are strongly lignified. 

Fig. 378. — The epidermis and a layer of cork cells cut transversely from 
the stem of Solanum dulcamara : a, the outer surface of the epidermis bearing 
a thick layer of cutin ; b, the walls of the cork cells infiltrated and covered with 
suberin. 



160 



PART II. — HISTOLOGY. 



maturity. In those cells which are united to form tissues the 
markings are seen as thickenings on the inner surface of the wall 
(see Figs. 371 to 378). They may form rings, spirals or reticula- 
tion , or they may be so arranged that the unthickened portions 
form circular or oblong disc-like markings. These, in old cells, 




Fig. 379. — Cells of Bottle Cork, showing polyhedral forms. 

frequently become perforations. The markings of cells will be 
more fully described when we come to treat of the different kinds 
of tissues. 

The cell-wall, besides increasing in thickness, grows also in 
surface area until it reaches maturity. Sometimes the growth 
is nearly equal in all directions, giving rise to spherical or sphe- 
roidal forms (Fig. 333), or if the cells are aggregated into masses, 
the tendency to an equiaxial growth may be modified by mutual 
pressure, producing cuboidal or polyhedral forms, Fig. 379; some- 
times the growth is greater in one direction than in any other, and 
elongated cells are the result; or, lastly, by a more exuberant 
growth in two or more different directions, tabular, star-shaped, or 
variously branching forms may be produced. Cork and epidermal 
tissues often afford examples of tabular cells. Fig. 380 represents 



CHAPTER I. — THE CELL. 



161 



a group of stellate cells from the stem of the Pickerel-weed, and 
Fig. 381, peculiar branching cells from the stem of the Yellow 
Water-lily. 




Fig. 380. — Stellate cells from the stem of the Pickerel Weed. 

Vegetable cells, on the average, are not more than one five- 
hundredth or one six-hundredth of an inch in diameter, though 




I ily. 



Fig. 381. — Branching cells (idioblasts) from the stem of the Yellow Water- 



162 PART II. — HISTOLOGY. 

in some cases they are large enough to be distinctly seen by the 
unaided eye, as in the flesh of the Water-melon and the pith of the 
Elder; in rare instances, as in the inter-nodal cells of Chara and 
Nitella, they may even be upwards of an inch in length. Some, 
on the other hand, are so small as to be barely visible under the 
highest powers of the microscope. This is the case with some 
Bacteria, and there is good reason to believe that there are organ- 
isms belonging to this type which no microscope yet made is 
powerful enough to resolve. 

As already stated, the primary cell-wall consists essentially of 
cellulose. An exception should be noted, however, in the so-called 
"middle lamella" which unites cell-walls derived from two adjoin- 
ing protoplasts into a common wall. The substance of the middle 
lamella appears to be of somewhat different composition, being 
more soluble in alkalies or chlorine solutions and more readily 
stained by aniline. In mature tissues the middle lamellae may 
remain as such, or may undergo a mucilaginous modification, or 
may even disappear altogether. 

On either side of the middle lamella are formed, first the pri- 
mary and later the secondary lamellae. These likewise result from 
the vital activity of the protoplasts. The primary lamella is 
usually of cellulose or some related substance, the secondary 
lamellae are frequently composed in part of modifications of cellu- 
lose. The wall substances, therefore, may be grouped as follows: 

Cellulose. Typical cellulose is recognized by its solubility in 
cuprammonia, its purplish coloration with zinc chloriodide and its 
blue color when treated with iodine and sulphuric acid. Reserve 
cellulose occurs in many seeds and is usually more readily acted 
on by enzymes and therefore more quickly available to the plant 
as food, than is ordinary cellulose. Amyloid, a closely-related 
body, is colored blue by iodine alone. 

Ligno-cellulose is the material composing "lignified" cell walls. 
It constitutes the great bulk of the wood of plants. Lignified walls 
consist of cellulose impregnated with several characteristic sub- 
stances known collectively as "lignin" and whose chemical nature 
is not well understood, but which give distinct colorations with 
certain reagents. Thus, phloroglucin and hydrochloric acid gives 
a cherry-red color with nearly all lignified walls. It is worthy of 
note that vanillin and some of the phenols occurring in plants 
give a coloration similar to that of lignin with the same reagent. 
With zinc chloriodide, lignified membranes assume a yellow color. 



CHAPTER I. — THE CELL. 163 

Cutin or suberin is a waxy substance which may impregnate 
only the outer portion of the cell-wall, as in the epidermis, where 
this layer is known as the cuticle, or may encrust the entire wall, 
as in the suberized cell-walls of mature cork cells. Cutinized or 
suberized walls are not dissolved by sulphuric acid, but are colored 
yellowish-brown by zinc chloriodide and yellow by potassium 
hydroxide. Such walls are practically impermeable to water and 
afford a protective covering to the plant. 

Mucilage. Cellulose walls may be partly or wholly converted 
into mucilage or gum. Examples are afforded by the seeds of 
Quince and Flax. If these seeds are placed in water, the outer- 
most cells are observed to swell, become transparent and finally 
dissolve to a thick mucilage. The inner cells of Chondrus and 
similar gelatinous algae undergo a mucilaginous modification. In 
some plants the cells of the pith, medullary rays and other por- 
tions of the parenchyma tissues may become mucilaginous. This 
is the case with the plants that yield the gums, Tragacanth and 
Acacia. Mucilage occurs also in special cells as well as in passages 
or canals formed by the cells breaking down (lysigenic) or split- 
ting apart (schizogenic). Such passages will be discussed in 
connection with the receptacles for secretions (see page 200). 
Mucilaginous walls may serve for water storage, or to assist in 
the distribution of seeds, or may constitute a form of stored food. 

Mineral substances. All cell walls contain an appreciable amount 
of mineral matter, which is, however, much greater in the older 
cells. The commonest mineral substances thus occurring are silica 
and calcium salts. Beautiful examples of the former occur in the 
cell-walls of Diatoms, where the silicification is very complete and 
the silicified walls are often very delicately sculptured. Notable 
amounts of silica also exist in the walls of many plant-hairs and 
in the ordinary epidermal cells of the Equisetums and many of the 
Grasses. 

Calcium carbonate, also, frequently occurs in the cell-walls of 
hairs, as well as in the cells of some seaweeds and in the curious 
structures called cystoliths, already mentioned. Calcium oxalate 
occurs occasionally as a crystalline deposit in the walls of thick- 
walled cells, as in those of Welwitschia (see Fig. 382), but more 
commonly crystals of this kind are found among the cell-contents. 

Stratifications. Thickened cell-walls are seldom homogeneous 
in structure, but if viewed in cross-section, they have the appear- 
ance of being arranged in concentric layers, as in Figs. 374, 376 



164 



PART II. — HISTOLOGY. 



and 383. This is called stratification, and the phenomenon is due 
to the alternation of layers of different water-content and some- 
times of different substance. Such thick-walled cells in longitu- 
dinal or surface view usually display delicate lines running 
obliquely, as shown in Figs. 384, 385 and 386. 

The term striation has been applied to this form of marking. 





Fig. 383. 



Fig. 384. 




Fig. 382. — Half of a thick-walled cell from 
Welwitschia mirabilis, showing crystals of 
oxalate of calcium imbedded in the cell-wall. 
(After Sachs.) 

Fig. 383. — Transverse section of bast fibers 
from the stem of Aristolochia Sipho, showing 
stratification. 

Fig. 384. — Portion of bast fiber, showing 
oblique striation. Highly magnified. 

Fig. 385. — Portion of bast fiber, showing transverse stria- 
tion. 

Fig. 386. — Bast fiber from the bark of Cinchona Calisaya, 
showing longitudinal striae and small tubes connecting the 
lumen of the cell with the exterior. 



Fig. 386. 



Fig. 382. 



In many cases, also, delicate, simple or branching tubes, called 
pore-canals, will be seen running from the cavity or lumen of the 
cell through the wall, Figs. 383 and 386. They doubtless facilitate 
the circulation of the sap from cell to cell. • 

Growth of the Cell Walls. Two theories have been presented to 
account for the manner of growth of cell-walls. One assumes 
that new particles of wall material are deposited within the 
already-formed membrane; this is termed growth by intussuscep- 
tion and satisfactorily explains the growth in surface area which 
can hardly be accounted for in any other way. In the second, 
termed growth by apposition, particles or micellae of wall substance 
are deposited on the surface of the cell-wall or successive layers 



CHAPTER I. — THE CELL. 165 

are superposed on it. It is scarcely open to doubt that the strati- 
fied walls such as those of bast fibers are produced in this manner. 

Practical Exercises. 

1. Upon the inner (concave) side of the bulb-scale of an onion, outline, 
with the sharp corner of a razor blade, a small square in the thin skin (epi- 
dermis), then strip off, with the forceps, this square portion of the epidermis, 
and place it in a drop of water at the center of a slide. Smooth out any 
wrinkles in the specimen by means of a camel-hair brush. 

Place a cover-glass over the specimen and examine with the low power of 
the microscope. A somewhat irregular network is seen, the meshes of which 
are elongated in one direction. Each of these meshes is a cell. 

The cells are made up of an enveloping membrane, the cell-wall and a 
glairy, viscid mass, the protoplast. 

The protoplasts appear colorless, transparent, and only slightly granular. 
In some a larger, rounded spot is faintly seen. Remove the slide from the 
stage, take off the cover glass and place a good-sized drop of iodine solution 
directly on the specimen. Clean the cover and replace it carefully, using the 
low power, observe that while the cell-walls have been scarcely stained, the 
contents have assumed a yellow-brown color, showing the cytoplasm and the 
nucleus in each cell quite distinctly. 

Again remove the cover glass and place a drop of zinc-chloriodide on the 
iodine-stained specimen. Using the same precautions as before, replace the cover 
glass and notice the effect of the stain. Excepting a thin layer of cutin on the 
outer surface, the cell walls appear purple-brown, due to the effect of the reagent. 
This is a test for cellulose, of which these walls are composed. 

Make a comparison study of the living cells of yeast, using iodine solution 
and noting the result as in the foregoing exercise. 

2. To observe the motion of the cytoplasm make a study of a young leaf 
from a growing branch of the Waterweed (Philotria canadensis). Mount the 
leaf entire in a drop of water. Use the low power first. The motion is usually 
more rapid in the long cells about the middle of the leaf. The green, disk- 
shaped granules (chloroplasts) move in the stream of cytoplasm and enable 
us to detect the motion more readily. Place the edge of a piece of filter paper 
in contact with the water in which the leaf is mounted and on the opposite 
border of the cover glass put a drop of iodine solution. The iodine will be 
drawn through and will stain the specimens, but will penetrate but slowly at 
first. Watch the effect of the reagent. Observe that the motion is stopped and 
that the chloroplasts are stained. Tiny black spots that may be seen in them 
are starch bodies. 

As a comparison study for the circulation of the cytoplasm, the hairs of the 
stamens from a young bud of Tradescantia, or a small piece of the green leaf 
of the Eel Grass (Vallisnaria spiralis) may be used to advantage. 

For the further study of chloroplasts, the thread-like cells of Spirogyra 
(Fig. 3'35), display the spiral, band-like arrangement while the prothalium of a 
fern shows large chloroplasts of the usual flattened and rounded type. 

An example of leucoplasts may be found in the cells of the cortical part 
of the Iris rhizome. 

Chromoplasts may be studied in the young petals of the common Nasturtium 
(Tropaeolum) or of the Larkspur (Delphinium). 

3. For the study of starch grains prepare a scraping of the inner flesh of a 
potato. Mount in water and view first with the low and then with the high 
power. In the field of view are seen numerous colorless, translucent grains, 
ovate, wedge-shaped, or almost spherical in form, and marked by a hilum, located 
excentrically, around which the layers of the grain are formed. The layers are 
narrower near the hilum and broader at the other end of the grain. If sufficient 
water has been used in mounting, the thickness of the grains may be demon- 
strated by tapping gently upon the cover-glass The motion of the cover-glass 
will cause the grains to rotate. It will then be seen that the grain is thicker 
through at the narrow end. If too great pressure be applied to the cover-glass 
the grains are fractured, the cracks radiating outward from the hilum, an evidence 
of their crystal-like structure. The effect of iodine solution should be noted. 
It may be best observed by allowing a drop of the reagent to run in under the 
cover-glass. Treatment with potassium hydrate solution causes the grains to 
swell, at first displaying the stratifications very distinctly, but these soon become 
lost to view. Note also the effect of boiling water upon the grains by carefully 



166 PART II. — HISTOLOGY. 



heating the starch suspended in a drop of water on the slide. Measurements 
with the ocular micrometer should be made, as well as drawings of several typical 
grains, care being taken to show the characteristic shape and form of the 
grains, and the location of the hilum and the stratifications. 

4. Food Starches, particularly those of the arrowroot, pea, bean, wheat, 
corn, oat and rice, should also be studied and drawings of them made. The pre- 
pared starches or the finely ground grains may be employed or the cereals may 
be softened in water and sectioned. The following descriptions and measure- 
ments should be verified : 

Arrowroot (Maranta arundinacea) somewhat resembles potato starch, but is 
smaller. Ovate, pear-shaped and broad fusiform are the chief forms. The hilum 
is usually at the broad end and marked by a two-rayed and curved cleft. Length, 
30 to SO microns. « 

Pea (Pisum sativum) and bean (Phaseolus vulgaris) contain starches that 
are oval, bean-shaped or kidney-shaped, little flattened and with distinct stratifica- 
tions. The hilum is replaced by a longitudinal and branched cleft. Length, 30 
to 40 microns in the pea and up to 60 microns in the bean 

Wheat (Triticum vulgare) starch shows the stratifications little or not at all, 
and the hilum can seldom be seen. The granules are of two sorts, the larger 
being the disk-like and flattened and about four times the diameter of the 
smaller roundish granules. Diameter of large granules, 27 to 40 microns. 

Corn (Zea mays) starch is of two sorts. That derived from the horny 
part of the grain is flattened and angular, that from the mealy part more rounded 
in outline. Both are similar in size, not distinctly stratified, and with a hilum 
showing a two, three or four-rayed cleft. Diameter of granules, IS to 30 microns. 
Smaller grains are few. 

Oat (Avena sativa) starch consists of rounded aggregates up to 60 microns 
in diameter, which break up readily into numerous small, sharply angular, many- 
sided grains, 2 to 8 microns in diameter. There are also small spindle-shaped 
forms which are of diagnostic value. 

Rice (Oryza sativa) starch is characterized by small polygonal grains, 2 to 
10 micron's in diameter, which form oval or rounded aggregates of from two to a 
hundred or more. 

Sago, tapioca, salep and cassava starches may also be studied in a similar 
manner. 

5. Drug Starches. Of the many characteristic drug starches only a few 
are selected for study. The commercial powdered drugs may be used or the 
pieces of whole drugs may be soaked in water until softened and then sec- 
tioned, or the dry drug may be scraped and the scrapings used as powder. 

Calumba (Jateorrhiza palmata) : The starch grains are variable in form, 
commonly pear-shaped, but often ovate, oval or roundish, and rarely compound 
in twos or threes. The hilum is frequently cleft, usually in the direction of the 
length of the grain. The stratifications are excentric and quite distinct. In 
size they average from 20 to 40 microns. 

Jalap (Exogonium purga) : There are present large, single starch grains of 
oval, circular or slightly flattened form, with broadly cleft hilum located excen- 
trically and with distinct though delicate stratifications, also compound grains 
in twos and threes, showing similar structure. Pasty, swollen grains are com- 
mon, these being probably due to the application of heat in drying the drug. 
The grains of Jalap starch measure 15 to 45 microns in diameter. 

Ginger (Zingiber officinale) : Grains biconvex, roundish, varying to three or 
four cornered, slightly longer than wide, each grain with a pointed end in which 
is located the hilum. Both the hilum and stratifications are difficult to see, the 
latter showing best in the larger grains. Length, 15 to 30, occasionally up to 
50 microns. 

Colchicum Corn (Colchicum autumnale) : Starch grains are of two sorts, 
the single grains being globular or egg-shaped in form, mostly with a stellately- 
cleft hilum, and faint but visible stratifications. The compound grains are in 
twos and threes and are similarly marked and of the same shape except when 
flattened by contact. Diameter of the largest grains about 20 microns. 

Ipecac (Cephaelis Ipecacuanha) : Grains mostly compound in twos, threes 
and fours, but numerous single grains are also present. The single grains are 
roundish in form with centric hilum and very faint stratifications. The hilum is 
frequently two or three-cleft. Each part of the compound grains displays similar 
markings. The single grains are from 6 to 13 microns in length; the compound 
attain a length of nearly 20 microns. 

Orris (Iris florentina, rootstock) : Starch grains elongated, oval or ovate, 
truncated, sometimes curved or lobed. Hilum located excentrically at the 
larger end of the granule and having usually a two-branched cleft extending 



CHAPTER I. — THE CELL. 167 



toward the smaller truncated end. Stratifications not distinguishable. Length. 
25 to 50 microns. 

6. Inulin may be viewed to advantage in sections of Taraxacum root or of 
Dahlia root which have been kept for a time in strong alcohol. Since inulin is 
soluble in water, the sections should be mounted in alcohol or glycerin. The 
inulin appears in sphaero-crystals. Note the effect of iodine solution and also of 
hot water on these crystals. 

7. For the study of aleurone grains, remove the testa (shell) of the Castor 
bean (Ricinus communis) and with a razor or sharp knife make very thin sec- 
tions of the kernel. Mount in glycerine and examine. The cells are filled with 
very small roundish granules. These are the aleurone granules. Run in under 
the cover-glass a drop of water and notice that when water acts on the speci- 
mens, globules of fixed oil are liberated and the aleurone grains gradually dis- 
solve. This oil occurs as one of the cell-contents associated with the aleurone. 
Test another section with iodine solution and note the result. 

Examine now a section of this seed which has been prepared by staining 
with an alcoholic solution of eosin for several hours previous to use. Mount the 
specimen in oil of cloves. Upon viewing with the high power some of the 
aleurone grains display a crystalloid of the same proteid substance as the granule 
itself and often one or more rounded bodies located at one end of the granule, 
the globoids. The crystalloids and globoids are surrounded by envelopes of 
amorphous proteid substance. 

Compare sections of the kernel of the Brazil nut (Bertholletia excelsa) sim- 
ilarly prepared and stained. Sections cut from near the surface but just under 
the cork tissue ("peel") of the Potato will show protein crystals of cubical form 
in the cells with starch grains. Sections of Fennel fruits (Foeniculum vulgare) 
may also be compared. (Fig. 351.) 

8. For the study of calcium oxalate crystals select a piece of the medicinal 
Squill, soften and prepare a thin section of the bulb-scale. View first with the 
low, then with the high power. Notice that the raphides occur either singly 
or in bundles, the latter being sheaf-like in form and grayish, owing to their 
cutting off most of the transmitted light. The solitary crystals are the larger 
in size, often extending through several cells, apparently piercing the transverse 
walls. The bundles of crystals are usually surrounded by a mucilaginous cover- 
ing soluble in water and which upon treatment with eosin solution is stained 
red. Make a drawing of each of these kinds and compare with them the 
raphides of the medicinal Ipecac and Sarsaparilla roots. Examine Soap Bark 
(Quillaja), making a scraping or thin section, mounting in water and observing 
the peculiar twin crystals. Rosettes crystals may readily be studied in the 
medicinal rhubarb, in which they are abundant, giving to the drug its charac- 
teristic grittiness. They may be viewed to advantage by mounting a scraping of 
the drug or a small quantity of the powder in chloral hydrate solution. 

Raphides are also abundant in the Evening Primrose, the Calla Lily, the 
Indian-turnip and most other members of the Arum family, as well as in many 
liliaceous plants. 

Sphaero-crystals are abundant in the Yellow Dock and in the Hollyhock and 
most other Malvaceous plants. 

Other forms may be found in the stems of the Cactuses, in the stems and 
leaves of the Begonias, in the leaves of the Century Plant, etc. 

Cystoliths of great beauty are obtained by making thin cross sections of the 
leaves of the common Nettle and of Ficus elastica. (Fig. 369.) 

These crystals may also be studied to advantage by means of polarized light. 

The following tests may be applied to determine the nature of the crystals : 

Acetic acid has no effect on silica and calcium oxalate, but calcium carbo- 
nate dissolves with effervescence. Hydrochloric acid has no effect on silica, but 
dissolves calcium oxalate without effervescence, and calcium carbonate with 
effervescence. 

9. To observe some of the various kinds of cell-walls and shapes of cells, 
examine a transverse section of the young stem of the Elder (Sambucus cana- 
densis), mounting the section in water. 

Notice that the stem is made up of cells differing from one another in size, 
shape, in the nature of their contents, and in the color and thickness of the 
walls. Cells of similar kind are arranged in groups or layers, and occupy definite 
portions of the stem. 

The outermost part of the stem is the epidermis, and beneath this is the 
cork, which may have replaced the epidermis, and is composed of several layers 
of tabular cells regularly arranged in radial rows. The walls of these cells are 
yellowish-brown in color, and are incrusted with suberin. 

Within the corky layer is located the middle bark, composed of cells which 
are iso-diametric, or nearly so, and have cellulose walls. Prove this by applying 



1G8 PART II. — HISTOLOGY. 



the zinc-chloriodide test. The outermost cells of this layer have very thick 
walls. 

The inner bark is composed of cells of two kinds. One has excessively thick- 
ened walls and a small cell cavity. These are the bast fibers. Their walls are 
lignified. To confirm this, mount a section of the stem in phloroglucin and 
hydrochloric acid. The walls of the bast fibers will be colored red, as will also 
the walls of the cells in the circle of wood surrounding the pith. Between the 
wood and the bast are severa layers of cells with cellulose walls. These con- 
stitute the phloem and cambium parts of the stem. In the vicinity of the bast 
in this stem are found glands filled with a transparent brown resin and others 
filled with tannin. 

The cells composing the wood are found, upon careful examination, to be of 
two kinds : tracheal tubes, with large cavities and relatively thin walls, and 
wood-fibers, with smaller cavities and thicker walls. Note also that the woody 
zone does not form a continuous circle, but is divided into numerous wedge- 
shaped parts, by rays of brick-shaped cells extending in a radial direction. 

Occupying the center of the stem is a pith, which consists of large, thin- 
walled iso-diametric cells. Usually tannin and resin sacs like those seen in the 
bark occur in the pith also. 

In the same manner, applying the reagents as before, examine tangential and 
radial longitudinal sections. Pay particular attention to the markings upon the 
cell-walls. Note especially the thin places (pores) in the walls of the pith cells, 
and the spiral and dotted markings upon the walls of the ducts. Compare the 
shapes of the cells as seen in the longitudinal sections with those seen in the 
transverse section. 



CHAPTER II.— THE FORMATION OF CELLS. 

Most cells have the power of reproduction, or of giving origin 
to new cells. This may take place either by cell division, which 
directly increases the number of cells, or by the formation of 
spores, which in turn give rise to new cells. 

Indirect Nuclear Division or Karyokinesis : In the higher plants, 
at least, cells increase in number by repeated and successive divi- 
sion. In this manner certain cells, styled primordial cells, give rise 
not only to the groups of similar cells known as tissues, but also 
to the aggregations of tissues comprised in the organs of the plant. 

Typical cell-division, in the vegetative cells of the higher plants, 
may be briefly outlined in two series of changes : those involved in 
the division of the nucleus and those resulting in the partition of 
the protoplast, usually through the formation of a cell-wall separat- 
ing the two daughter cells. The close inter-relation between these 
two series of changes adds to the difficulty of a clear understanding 
of this phenomenon. 

The successive changes in the nucleus are as follows (see Fig. 
387) : 

The threads forming the reticulum of the resting nucleus are 
shortened and thickened, while the chromatin particles swell and 
become disk-shaped. The thickened skein thus formed and repre- 



CHAPTER II. — THE FORMATION OF CELLS. 



169 



senting the reticulum is converted into a definite number of 
"chromosomes" which assume the form of hooked rods of L or U 
shape and which are then arranged in a plane with the curved 
ends facing the plane and thus forming the "equatorial plate." 







>^&raS*&7) 




■•■■;•■ / 


Tep 







1 




ffl- 


3i : :-ip-.^r^ 



Fig. 387. — Successive stages of nuclear and cell division in a meristematic 
cell. n. nucleus; nl. nucleolus; w. nuclear membrane; e, cytoplasm; ch, chromo- 
somes; k. polar caps; s. spindle; kp. nuclear plate; t, young daughter nucei ; 
v, connecting fibrils; z, cell-plate; m. new cell-wall. In 1, the resting nucleus; 
2 and 3, separation of the chromosomes: 4, chromosomes with transverse discs; 
5, the arrangement of the chromosomes to form the cell-plate and their longi- 
tudinal fission ; 3-5 show the formation of the spindle from the polar caps ; 6. 
the longitudinal fission of the chromosomes; 7, beginning of their separation to 
either pole; 8, the complete separation of the daughter chromosomes; 9, passage 
of the daughter chromosomes to either pole; 10-12. formation of the daughter 
nuclei; in 9-11 the origin of the connection fibrils and of the cell-plate is seen, 
while in 12 the new cell- wall is formed, f Strasburger.) 

Meanwhile each chromosome has split lengthwise into halves, 
which pull away from each other in opposite directions. 

While these changes are taking place, the delicate protoplasmic 
membrane surrounding the nucleus has developed fibrils at 
opposite sides, forming the "polar caps." Similar fibrils within 
the nucleus are attached to the chromosomes and facilitate the 



170 



PART II. — HISTOLOGY. 



construction of the equatorial plane. These protoplasmic threads 
soon extend from the polar caps to the chromosomes and also as 
continuous fibrils from pole to pole, giving rise to the "nuclear 
spindle." 

The split chromosomes are now moved along the fibrils of the 
spindle, but in opposite directions, as above mentioned, to the poles, 
where they constitute the chromosomes of the "daughter nuclei" 
and, uniting with one another, resume the reticulate structure 
characteristic of the resting nucleus. The nucleoli take no active 
part in this process ; apparently they serve chiefly for nourishment 
and to provide material for the fibrils. The form of nuclear divi- 
sion above outlined is termed indirect nuclear division, mitosis, or 
karyokinesis. 

Its undoubted advantage is in making sure of an equal division 




Fig. 388. — Commencing development of partition-walls between the nuclei 
produced by successive divisions in the embryo-sac of Agrimonia eupatorium 
(after Strasburger). 



of the nuclear substance between the two daughter cells, especially 
an equal distribution of the chromosomes, which evidently transmit 
the characters of the parent cell to the offspring. 

After the formation of the two daughter nuclei, the fibrils of 
the spindle expand so as to give the mitotic figure a barrel shape, 
with the nuclei at the heads of the barrel. Along a plane passing 
through the middle of the barrel-shaped figure, the fibrils are 
thickened and finally fused, forming the "cell-plate," which is at 



CHAPTER II. — THE FORMATION OF CELLS. 171 

first a homogeneous protoplasmic membrane, but later splits into 
two layers, between which the new cell-wall forms. 

The segmentation of the mother cell into the two daughter cells 
is now complete and the remaining fibrils gradually merge into 
the cytoplasm of the new-formed cells. 

A modification of the process above •outlined occurs in the 
course of the growth of the endosperm in the embryo-sac of angio- 
sperms, where by rapid division after fertilization a large number 
of nuclei are formed, each connected with its neighbors by a spin- 
dle of fibrils, but with at first no permanent cell-plates; at a later 
stage of the growth of the embryo, cell-walls are developed and 
the subsequent multiplication of cells is through the typical divi- 
sion already described (Fig. 388). 

Another modification of the typical form of nuclear division is 
observed in the reproductive cells constituting the so-called "spor- 
ogenous" tissues, which give rise to spores. Of such nature are 
the "mother cells" of the anther, where the pollen grains (micro- 
spores) are formed. This is termed reduction division. 

While in the vegetative reproduction, above described, there is 
but one thread in the reticular skein, and this, presumably, bears 
all the transmissible characters, in reduction division there are two 
parallel threads forming the skein, one of these supposedly bear- 
ing the paternal, the other the maternal characters. In suitably 
stained preparations these threads are seen to be composed of 
alternating colored (chromatin) and colorless (linin) bodies. 

After passing through some intermediate phases the double 
threads divide transversely into segments, and since each of these 
segments represents a pair of chromosomes, they are, of course, but 
half as numerous as the single chromosomes formed in the vegeta- 
tive cells of the same plant. Several more phases follow, but 
finally the paired chromosomes are lined up at the equator of the 
cell, the paternal members of the pairs are drawn to one pole, the 
maternal members to an opposite pole. On the way to the pole each 
chromosome divides longitudinally, and, arriving at the pole, the 
split chromosomes spin a nuclear reticulum which becomes enclosed 
in a nuclear membrane and forms the nucleus of the "daughter" 
cells. 

The split chromosomes then reappear, the halves are separated 
in a manner similar to ordinary nuclear division and formed into 
nuclei of the granddaughter cells, there being now four of these, 



172 



PART II. HISTOLOGY. 



which have been produced from the original mother cell and which 
now become the spores or gametes (Fig. 389). 

As distinguished from these forms of cell-division we find in 
some of the lower plants other processes, among which are: 

Free Cell Formation, where the nuclear division of the ordinary 




Fig. 389. — Dividing pollen mother cells of a Lily, somewhat diagrammatic. 
1, mother cell, with resting nucleus; 2, the separation of the chromosomes; 3, 
the condition of contraction known as synapsis ; 4, double filament in process of 
fusion ; 5, spirem consisting of an apparently single filament derived from the 
fused double filament ; 6, reappearance of the longitudinal split, the spirem still 
unsegmented ; 7, spirem transversely segmented, into paired chromosomes ; 8, 
diakinesis ; 9, multipolar spindle; 10, spindle of the mother nucleus, the nuclear 
plate composed of paired chromosomes; 11, reduction divisnn, the separating 
chromosomes showing partial separation of their longitudinal halves; 12, young 
daughter nuclei ; 13, the longitudinal halves of the chromosomes (daughter 
chromosomes) are arranged in pairs on the nuclear spindles; 14, th" spindles 
of the daughter nuclei; 15, separation o fthe daughter chromosomes ; 16, young 
stage of the grand-ilanghter nuclei. (Strasburger.) 



CHAPTER II. — THE FORMATION OF CELLS. 



ITi 



type is followed by the formation, in the cytoplasm of the mother 
cell, of a wall surrounding each nucleus, the walls of adjoining- 
cells not being in contact with each other. The spores of the 
Ascomycetes illustrate this method of cell formation (Fig. 390). 





Fig. 391. 

Fig. 390. — Small portion of sporocarp of 
Cup Fungus, showing asci containing asco- 
spores produced by free cell formation. 

Fig. 391. — Various stages of cell budding 
in Yeast Plant (after Reess). 



Budding — is another method of cell division. In this, a minute 
protuberance is formed on the surface of the cell; it gradually 
increases in size until it may be as large or nearly as large as the 
parent cell, when usually it separates through constriction and 
becomes an independent organism. The Yeast plant affords an 
example of this mode of propagation (Fig. 391). The spores 
known as conidia, produced by other Fungi, originate similarly 
(Fig. 392). 

Direct nuclear division, alto termed amitotic division or frag- 
mentation, occurs but seldom and is observed chiefly in old cells. 
It comes about through a constriction of the nucleus, resulting in 
its division into two sometimes unequal nuclei and is not followed 
by cell-division such as attends indirect nuclear division. 

It will be seen that in all cases new cells are formed from pre- 
existing ones; that living organisms are derived from antecedent 



174 



PART II. HISTOLOGY. 



living organisms. The spontaneous generation of living proto- 
plasm from inorganic matter has never yet been observed. 



>v // 




Fig. 392. — Conidiophores of Aspergillus herbariorum (at left) and Penicil- 
lum crustaceum Cat right). 



Practical Exercises. 

1. Sterilize by boiling in water several pieces of blotting paper. After these 
have cooled but are still moist place on them a few small onions and cover with 
a bell jar. When the onions have sprouted and the roots are about an eighth 
of an inch long, cut off several roots and "fix" them in Flemming's fixative. 
Imbed in cellodin or paraffin and cut longitudinal sections, or if this is not 
feasible, cut transverse sections, free-hand, by holding the roots between pieces 
of elder pith. Stain the sections with Flemming's triple stain (safranin, gentian- 
violet and orange G.), dehydrate and mount in Canada balsam. (For details 
of these processes see Stevens' Plant Anatomy, third edition, pp. 258 to 278). 
The sections should show nuclear cell division and should be compared with the 
description given in the text (p. 169), also with the description of a typical 
cell (p. 132). 

2. Select a young staminate flower bud of Begonia and make thin sections 
with a moistened razor across the upper part of the bud, including the tips of 
the contained anthers. Pick out several of the thinnest sections, including the 
anthers, and transfer them carefully to a drop of water on a slide. With the 
aid of a magnifier remove all but the thinnest sections of the anthers themselves. 
Cover and study under the microscope. With the low power, observe the two 
cavities in each of the two anther sacs. Later these coalesce. Note the isolated 
rounded cells either in the cavities or floating in the water. These are the 
pollen mother-cells. 

3. Select another staminate flower somewhat older than the preceding and 
prepare sections in the same manner. Stain with iodine solution. With the aid 
of the low power find some of the pollen mother-cells floating in the water, and 
focus on them with the high power. Observe the contents of each mother cell, 
four small pollen grains. Note the form of the grains, the nucleus in each 
grain and the readiness with which the cytoplasm takes the stain. Compare 
several fully developed pollen grains from the ripe anther of a full-blown flower. 

4. Make a culture of yeast by preparing a broth consisting of three table- 
spoonfuls of mashed potato and one tablespoonful of sugar in a pint of water. 
Bring to a boil and when cool add a piece of yeast cake and set the culture 



CHAPTER III. — THE TISSUES. 175 



aside in a warm place for several hours until the formation of numerous bubbles 
indicates that the yeast is "working." 

Examine a drop of yeast under a magnifying power of 600 or 700 diameters. 
Budding cells will be observed, with the buds in various stages of development. 
Make drawings of some of them. 

Obtain a piece of porous tile ; place one end of it in a small dish con- 
taining water. The portion not immersed will be kept moist by capillary attrac- 
tion. On this portion place a little yeast; cover the whole with a bell jar; keep 
in a moderately warm place for a few days, and th.en examine the yeast. Some 
cells will probably be found in which the protoplasm has broken up into several 
small, rounded masses, presenting an example of internal cell-formation. 

Obtain in spring or early summer, when vegetative growth is rapid, some 
filaments of Spirogyra ; examine them microscopically by daylight, and note 
that the cells all appear well developed, and no signs of cell-division are observ- 
able. This is because in these plants the cell-division takes place in darkness. 
Let the filaments remain in water in a dark room until after midnight ; then 
place them in 60 per cent alcohol, which will stop their growth and kill the 
protoplasm. Now study them microscopically, and cells will be found in all 
stages of division, some in which the nucleus has just divided, and an artnular 
protuberance on the interior of the cell- wall, (the beginning of a cellulose 
septum) has made its appearance ; others in which the division is nearly com- 
pleted, and still others in which the separation into two cells is quite complete, 
but the new cells have not yet attained their full growth. 

Make drawings of different stages in the process. 

The little red Cup-fungus, Peziza coccinea, is not uncommon in our woods. 
Make a thin, vertical section of the "cup" or hymenium of one of these plants, 
and examine with a magnifying power of 300 or 400 diameters. Numerous 
elongated cells, each containing a number of oval spores, called ascospores, will 
be observed. Some of the latter may be seen escaping from the top of the asci, 
or mother cells. Draw one of the asci with its contained ascospores. 



CHAPTER III.— THE TISSUES, THEIR ORIGIN AND 
CLASSIFICATION. 

While it is true that all the essential phenomena which we call 
"vital" are manifested within the compass of a single cell, it is 
true, also, that the manifestation is feeble in comparison with that 
exhibited by cell aggregates, where there is division of labor among 
the cells. All the higher plants are such aggregates or collections 
of cells. A Rose-bush, for example, is made up of millions of them, 
and its life is not the mere aggregate life of cells precisely alike, 
but rather that of sets of cells that have grown to differ from each 
other in form and function, some being specialized for one use, and 
others for another, but all subserving the life of the whole organ- 
ism. These cell-groups, which differ from each other in ways more 
or less important, but each of which is composed of similar cells, 
are called tissues. The lowest plants can hardly be said to possess 
tissues, since they' are either one-celled or are collections of pre- 
cisely similar cells; but as we study plants in the ascending scale, 
we find a more and more complete differentiation of the cells, until, 
in the ferns and flowering plants, we find a great variety of tissues. 

Tissues may conveniently be classified into five groups, the 



176 PART II. HISTOLOGY. 

Dieristematic, the parenchymatous, the prosenchymatous, the sieve 
and the secretory. 

Meristematic Tissue. As already pointed out, tissues arise by 
repeated cell-division. This process must underlie the development 
of all new plant parts. Cell-division begins at certain points, 
usually the apical cells, at the end of the stem or branch, or just 
back of the cap of the root. From these apical cells are formed 
by cell-division a mass of undifferentiated tissue known as the 
primordial meristem. From this is developed the primary meri- 
stems, which in turn give rise to primary permanent tissues.- 
Meristems, then, precede the formation of the permanent tissue, 
whose cells are mature and fully differentiated. We may therefore 
regard meristematic tissue as simply the embryonic or undifferen- 
tiated tissue from which all the later tissues are derived; yet it is 
sufficiently characteristic to be entitled to a place as a definite 
tissue. 

If we study a longitudinal section of the growing tip of a young 
stem or shoot, or a young root just behind its cap, we will observe 
that the cells of the growing plant are very small, much alike, 
densely filled with cytoplasm and contain relatively large nuclei 
(see Fig. 333). We will find no sharp demarcation between this 
homogeneous mass of cells and somewhat differentiated layers 
which closely border upon it. As we pass back from the growing 
point, however, the tissues become more distinctly differentiated. 
Evidently, then, the cells originate in the growing point, where 
they are exceedingly minute and densely filled with cytoplasm; 
then they absorb water osmotically, their walls are stretched by 
the expanding sap-cavity, new wall substance is deposited, the cell 
groivs, extending in the direction of the least pressure; at length 
the cell is full-grown, is many times larger than its original size, 
its wall is tightly stretched and in close contact with adjoining 
cells ; it has attained certain distinctive size, shape and wall-mark- 
ings and has become one of the units of a permanent tissue. 

As already stated, primary meristems are located, with few 
exceptions, at the apices of plant organs and give rise to primary 
permanent tissues; secondary meristems, on the other hand, form 
from living primary permanent tissues and give rise to secondary 
permanent tissues. The former determine the growth in length of 
a stem or root, the latter control its later growth in thickness. A 
good example of a secondary meristem is afforded by the so-called 
"cork-cambium" or phellogen that forms in the cortical paren- 



CHAPTER III. — THE TISSUES. 



177 



chyma and gives rise to the cork, which is purely a secondary 
tissue (see Figs. 420 and 421). 

Parenchymatous Tissues. Tissues whose cells generally retain 
to maturity the characters of living cells, that is, they possess 
cytoplasm and nuclei as well as more or less plastic material, are 
known in general as parenchymatous tissues. Their cells are 
usually isodiametric or nearly so, at least they are as a rule not 
greatly elongated, and are mostly joined together by their flattened 
sides, therefore not fibrous nor interwoven. Ordinarily, the cell- 
walls of these cells are thin and composed of cellulose. However, 
here, as alsewhere in nature, many gradations and transitional 
forms occur, so that hard and fast lines are difficult to draw. 
Included in this group are Parenchyma, Collenchyma, Sclerotic, 
Epidermal, Endodermal and Cork tissues. 

Parenchyma, the simplest form of permanent tissue, is the most 
abundant as well as the most important of all the tissues. The 
cell-walls are thin, and frequently, though not always, composed 
of unmodified cellulose. In form, the cells are commonly spheroidal 
or polyhedral, and the longitudinal diameter rarely much exceeds 
the transverse (see Fig. 393). 




Fig. 393. — Typical parenchyma from rhizome of Podophyllum. 



178 PART II. — HISTOLOGY. 

Parenchyma includes most of the softer tissues of plants, 
such as the green cells of the leaf, the thin-walled cells of the 
pith, a considerable portion of the cells of the bark, frequently 
those of the medullary rays, etc. Not infrequently the* cell-walls 
are so unequally thickened as to present the appearance of mark- 
ings or sculpturings of various kinds; indeed, they are seldom of 
uniform thickness, but commonly their membranous character and 
transparency makes them appear so. Forms of parenchyma are 
shown in Figs. 371, 372, 380, 393 and 394. 

The very loosely arranged green cells that occur in the interior 
of leaves constitute the spongy parenchyma (Fig. 415) ; the more 
compactly arranged and somewhat elongated ones found next the 
upper epidermis of most flattened leaves, the palisade parenchyma 
(Figs. 369 and 415) ; parenchyma like that illustrated in Fig. 394 
is called pitted parenchyma; that in which the cells take star- 
shaped forms, as shown in Fig. 380, is called stellate parenchyma; 
and the green cells with internally folded walls, found in the 
interior of Pine leaves, are called folded parenchyma (see Fig. 
489). 

Parenchyma tissues, being widely distributed, perform various 
functions. The chlorophyll-bearing parenchyma of leaves is the 
chief photosynthetic tissue; the conducting parenchyma, associated 
with the vascular bundles, conveys elaborated foods in solution; in 
the reserve parenchyma of the fleshy parts of plants, foods are 
stored, usually as cell contents, as already noted, but occasionally 
as thickened walls, notably in the seeds of the date and the vege- 
table-ivory nut. 

Collenchyma is a tissue nearly related to parenchyma, from 
which it differs chiefly in the peculiar thickenings of its cell-walls. 
The cells composing collenchyma tissue are closely connected, are 
from three to eight sided, several times longer than wide and with 
horizontal or obliquely-pointed ends. The cell-walls are thinnest 
at the ends and at the middle of the sides and are thickest at the 
angles, where three or four cells meet, the thickened walls being 
whitish, lustruous and delicately stratified. In typical collenchyma 
this thickening is due to deposits of cellulose and the cells usually 
contain cytoplasm, nuclei and more or less chlorophyll. No sharp 
lines of distinction can be drawn between parenchyma arid collen- 
chyma, as there exists every gradation between these tissues. 

Collenchyma is never found elsewhere than in close proximity 
to the epidermis, or rarely in similar relations to the endodermis, 



CHAPTER III. — THE TISSUES. 



179 



and one of the uses which it serves is evidently that of giving 
strength and resistance to these portions of the plant. Being 
unlignified and elastic, it is well adapted for young and growing 
parts. Sometimes it forms a continuous zone beneath the epider- 




Fig. 394. — Pitted Parenchyma from the pith of the stem of the American 
Papaw. 




Fig. 395. — Portion of epidermis of collenchyma from stem of Yellow Dock. 
Transverse section, ep. epidermis ; c, collenchyma. 



ICO • PART II. HISTOLOGY. 

mis; at others, it occurs in longitudinal bands. The tissue is illus- 
trated in Figs. 373, 395 and 411. 

Sclerotic Tissue. The cells of this tissue are commonly called 
stone or grit cells. It differs from ordinary parenchyma in having 
the walls of the cells excessively thickened — so much so, frequently, 
that the cavity of the cell is nearly obliterated. Every gradation, 
however, may be observed between these and ordinary parenchyma 




Fig. 396. — Sclerotic cells from the flesh of the Pear. 

cells. In sclerotic tissue the cell-wall is usually lignified, and the 
thickening is in layers, presenting the appearance of stratifica- 
tions. There are also delicate tubes or pore-canals radiating from 
the cell-cavity to the outer portion of the cell-wall. 

These are the cells which give the great hardness to the outer 
coats of many seeds, and the shells of nuts. They constitute the 
gritty particles that occur in the flesh of some fruits, as that of 
the Pear. They occur in Cinnamon and Cinchona barks and in 
Tea leaves, and are, in fact, seldom entirely absent from the more 
highly organized plants. See Figs. 356, 374, 396, 397, 398 and 399. 

Stone cells are sometimes grouped with wood fibers and bast 
fibers under the general name of Sclerenchyma or of Stereome. 
In this event the stone cells are distinguished as Short Scleren- 
chyma, the fibers as Long Sclerenchyma, the distinction being 
based on the fiber-like form and the greater length (0.5 to 2 mm.) 
of the latter. 

Epidermal Tissue. All of the higher forms of plants possess an 
outer layer of cells sharply defined by their shape, size and often 
color from the tissues within, and constituting the epidermis. 

This tissue consists usually of but a single layer of tabular or 
plate-like cells arranged compactly side by side, with no inter- 



CHAPTER III. — THE TISSUES. 



181 



cellular spaces except where stomata and water-pores are situated. 
Occasionally we find underlying and strengthening layers consti- 
tuting a hypodermis (see Fig.' 400). A typical epidermal cell such 
as occurs on the more permanent aerial parts of the plant is a 
little longer than broad, has a comparatively thin inner wall, 




Fig. 397. — Sclerotic cells from the shell of the Cocoanut (Winton) 

somewhat thickened and often wavy side walls and a very thick 
outer wall. The thickening of the outer wall is due to an adhering 
film of cutin, coating its outer surface. This film is the cuticle 
(Figs. 369 and 378). It is usually distinctly stratified and is 
occasionally coated over with a reinforcing layer of wax or even 
of silica. On the floral parts and in the epidermis of young roots 
it is commonly absent. The nearly or quite waterproof cuticle is 
an effective means of preventing loss of water, while it is scarcely 
less efficient against the attacks of parasitic fungi. 

Epidermal cells usually contain cytoplasm and often have 



182 



PART II. — HISTOLOGY. 



coloring matter dissolved in the cell-sap. Chlorophyll is rather 
seldom present except in guard cells. Not infrequently the epider- 
mal cells of the upper surface of leaves show a lens-shaped swell- 
ing or papilla; these possibly act as condensing lenses to collect 
the light-rays and thereby promote photosynthesis. Similar but 
rather more elevated papillae characterize the velvety surface of 




Fig. 398. — Sclerotic cells from Tea leaves. 

many petals (Fig. 406). In certain tendrils, the epidermal cells 
possess a tactile sense that is remarkable. 

The hypodermis may assume some of the functions of the epi- 
dermis, restricting the latter to the protective and waterproof 
functions merely, as in some Pine "needles" (Fig. 489). In other 
instances the hypodermis serves only a mechanical purpose, but 
most commonly it is directly concerned with the storage of water. 

The epidermis remains, as a living tissue, until it is cut off 
from its supply of water by the development of cork (Fig. 378). 

Stomata are composed of modified epidermal cells, usually 
crescent-shaped and chlorophyll-bearing, occurring in pairs with 
the concave sides facing so as to leave an opening between. Each 
cell is called a guard-cell and the entire organ is a stoma (Fig. 



CHAPTER Hi.— THE TISSUES. 



183 



402). In the tissue directly beneath the stoma is always found an 
intercellular space which communicates with intercellular 
passages throughout the leaf. (Fig. 403.) 



air 




F : g. 399. 



£ ig ' inn'~<? cler0tic Cells from Wild Ch errv bark 
hairs andTfo^ r00t ' showin S e P idermis - consisting of 




and stomttl-^moTocotyl It * ^ Sh ° Wing a SUrface view * f epidermal cells 



184 



PART II. — HISTOLOGY. 



Stomata are the most common upon the green parts of plants, 
especially leaves, but may occur upon any of the plant organs 
except roots. In leaves, stomata are usually more numerous upon 
the shaded surface. As a rule, the stomata are arranged in rows 




No. 402. — Epidermis of Tulip leaf, showing a surface view of a stoma under 
high magnification. 



in Monocotyledons and are irregularly arranged in Dicotyledons 
(see Figs. 401, 402, 403, 404, 405). 

The number of stomata varies much in different species of 
plants. On the under surface of bifacial leaves the number will 
average from one hundred to three hundred in a square millimeter, 
but in some plants the number may reach seven hundred, indicat- 



CHAPTER III. — THE TISSUES. 



185 



ing that a half a million stomata may be present upon a square 
inch of leaf surface. 




No. 403. — Epidermis of the Tulip leaf in transverse section, showing a stoma 
and adjacent epidermal cells, also intercellular spaces and chlo/enchyma. 

Stomata have the power of opening and closing under the 
influence of light, warmth and moisture, and act as automatic 




No. 404. — Epidermis and stoma of the Tulip leaf in perspective view. 

valves to regulate the amount of moisture given off by the leaf 
as well as to allow free access of air to the interior. 



186 



PART II. — HISTOLOGY. 



Stomata are formed by division of the epidermal cells, first a 
stoma mother cell is produced, then this divides into the two 
guard-cells which split apart, providing the pore. 

Water-pores or hydatodes are also openings in the epidermis, 
bearing some resemblance to stomata, but differing from them in 




No. 405. — Epidermis from the lower surface of Stramonium leaf, showing 
cells and stomata under high magnification. 

the fact that the guard-cells are immovable, and the opening, 
therefore, does not increase or diminish, and also in the fact that 
water, instead of gaseous matter, commonly fills the orifice or 
oozes out upon the surface. Their distribution is also different 
from stomata. While the latter are most abundant between the 
veins on the under surface of leaves, water-pores occur at the 
extremities of veins on the margin of the leaf and usually toward 
the upper side. Fig. 407. 

Trichomes or plant-hairs are modifications of epidermal cells, 
being formed by such cells projecting or lengthening outward. 



CHAPTER III. — THE TISSUES. 



187 



They occupy a position intermediate between papillae, which repre- 
sent only slight projections of the epidermal cells, and various 
emergences in which the tissues underlying the epidermis are 
more or less deeply involved. Trichomes vary in character; some 
are single-celled, others are many-celled; some are simple in shape, 




No. 406. — Epidermis of the petal of Cranesbill, showing epidermal cells with 
folded walls and papillae, also a glandular trichome. 



others are variously branched and forked; some are microscopic in 
size, others, like cotton, are more than an inch in length. They 
may be borne upon any organ of the plant, that is, upon root, 
stem or leaves, and they usually occur without definite order. 

Unicellular trichomes, or those consisting of but one cell, are 
the more common. These, though usually undivided, may be 
forked, branched or stellate (Figs. 408, 409, 410 and 411). Multi- 
cellular trichomes, those built up of several or many cells, may be 
moniliform (necklace-like) clavate (club-shaped), capitate (with 
a gland-like head), hooked, stellate, peltate, etc. (Figs. 411, 412, 
413, 414, 415, 416 and 417). The cell-walls of plant-hairs may 
consist of unmodified cellulose or may be cutinized, silicified or 
even lignified. The cell-contents may include protoplasm, cell-sap 



188 



PART II. — HISTOLOGY. 



and, in the glandular trichomes, oil, resin, wax or irritating sub- 
stances. Trichomes which have lost their living contents and have 





Fig. 407. 

Fig. 407. — Section of leaf of a species of Saxifrage, showing two water-pores 
at the extremity of a vein. Above them are two hairs, to which usually a deposit 
of calcium carbonate clings, on evaporation of the water excreted by the pores. 
(Modified from Vines.) 

Fig. 409. — Simple unicellular hairs from Vaccinium Aictostaphylos leaf. 
(Mueller.) 




Fig. 409. 

Fig. 409. — Branched unicellular hairs from 
Aubretia deltoidea. (Kernerand Oliver.) 

Fig. 410.— -Spiral unicellular hairs from Cen- 
taurea Ragusina. (Kerner andOliver.) 



Fig. 410. 
become filled with air, being therefore white in appearance, are 
not uncommon. 




CHAPTER III. — THE TISSUES. 



189 



Most important to the plants are the trichomes growing near 
the tips of the roots, for these, by osmosis, absorb water and nutri- 
tive substances from the soil. 

Trichomes afford an important means of lessening water loss 
through transpiration, particularly when felted or woolly; they 




Fig. 411. — Epidermis and sub-epidermal collenchyma from the petiole of 
Abutilon avicennae. showing simple and multicellular hairs. 



may also become a means of seed distribution, — especially hairy 
outgrowths of the seed coat, like those of the Milkweed; they may 
serve for defense against insects or herbivorous animals, — the 
prickles of the Cactus species being notable instances, or as an 
aid in climbing, or they may serve for the secretion of various 
principles, such as the perfume of flowers. Secreting hairs are 
distinguished as "glands," but this term includes also protuber- 
ances of quite complex structure but of similar function. 

As their form, size, contents and cell-walls are ofter charac- 
teristic, trichomes are of great value in the recognition of drugs, 



190 



PART II. — HISTOLOGY. 



especially as they usually retain their identity, even after the 
plant or organ bearing them is powdered. 




Fig. 412. Fig. 413. 



Fig. 414. 



Fig. 412. — Moniliform hair from the stamen of Tradescantia. 

Fig. 413. — Moniliform hair of Mirabilis Jalapa. 

Fig. 414. — Different kinds of barbed hairs from leaf of Mentzelia ornata. 

Endodermal Tissue. This tissue consists of a single layer of 
compactly arranged cells which surround and form a protecting 
sheath to either single fibro-vascular bundles or, more rarely, to 
groups of them. This sheath is known as the endodermis. The 




Fig. 415. — Leaf of Shepherdia canadensis, showing pal : sade and spongy 
chlorenchyma and epidermis with many peltate trichomes. 

cells composing it are commonly elongated, four-sided prisms, with 
square or oblique ends and often with cutinized walls. The cutini- 
zation is usually most evident in the radial walls — those which 



CHAPTER III. — THE TISSUES. 



191 



are common to adjoining cells. In one type of endodermis this 
portion of the wall is more or less wrinkled or folded. Besides its 
protective function the endodermis also serves to restrict the 
translocation of food substances to certain paths and to prevent 
their escape from the conducting bundles into the surrounding 
tissues. See Figs. 418, 460 and 461. 




Fig. 416. — Epidermis of Stramonium leaf, showing verrucose and glandular 
multicellular hairs. 



Cork or Suberous Tissue. The cells composing this tissue are 
rectangular, usually tabular, and placed in rows one behind 
another with their side walls forming continuous lines correspond- 
ing to radii of the stem. Ordinarily no intercellular spaces exist 
in cork tissue. Cork cells originate in a secondary meristem, the 
phellogen, the cells of which divide tangentially in a very regular 
manner (Figs. 420 and 421). The cells of the phellogen and those 
cells within it contain cytoplasm. The mature cork cells exterior 
to it have lost their living contents and are filled with air (Fig. 
419). The walls of the mature cork cells consist wholly or in part 
of suberin, a substance nearly identical with cutin; occasionally 
they are lignified, resembling sclerotic cells (stone-cork). The 



192 



PART II. — HISTOLOGY. 



cork cells of different plants may vary characteristically in size 
ar>4 »hape, as well as in the thickening and color of their cell-walls. 




Fig. 417. — Branched multicellular hairs of Mullein leaf. (Kerner and Oliver.) 




Fig. 418. — Transverse section of Couch-grass rhizome, showing the endo- 
dermis (2) adjacent to the wood bundles (3) and parenchyma (1 and 4). 

Cork is a secondary tissue located just under the epidermis, 
which it frequently replaces. It may extend backward into the 



CHAPTER I! 



-THE TISSUES. 



193 



middle and even the inner bark. Normally, cork occurs abundantly 
in the perennial stems and roots and rarely in the leaves of dico- 
tyledons, less frequently in monocotyledons and very seldom in 
cryptogams. 








Fig. 419 . 



Fig. 420. 



Fig. 419.— Section of branch of Currant, showing cork cells, and the way 
they are formed, c. chlorophyll-bearing parenchyma ; b, cork-cambium ; a, mature 
cork cells. 

Fig. 420. — Section of bark of Cascara Sagrada, showing, 1, mature cork 
cells; 2. immature cork cells; 3, phellogen ; (4) mother cells. 

The function of cork, like that of the epidermis, is to protect 
the tissues lying beneath from too great evaporation or from 
injury; "Wound Cork," which forms when the living tissues inte- 




Fig. 421. 




big. 422. 



Fig. 421. — Section of stem of Elder, showing, 1, mature cork cells; 2, imma- 
ture cork cells; 3, phellogen; 4. mother cells. 

Fig. 422. — Transverse section of bast cells from the stem of Menispermum 
canadense. The middle lamella is shaded dark, and the walls of the thickened 
fibers show concentric lamination. 

rior to the epidermis are laid bare, serves this purpose of protec- 
tion very effectively. Leaf scars are also protected by a growth 
of cork. 



194 



PART II. — HISTOLOGY. 



Prosenchymatous Tissues. Those tissues are often grouped as 
Prosenchyma, whose cells, at maturity, lose their nuclei and proto- 
plasmic contents, and therefore their distinctively living character, 
and have their walls thickened by secondary deposits, usually of 
lignin. Such cells are for the most part elongated and oblique- 
ended or taper-pointed and are joined together by their sides and 




Fig. 423. — Longitudinal view of small portions of the long bast fibers from 
the stem of the same plant, showing oblique markings in the cell walls. 

by their oblique and tapering ends. They sometimes contain starch 
and traces of proteid matter, but take no active part in the nutri- 
tive processes of the plant. These tissues serve chiefly for strength- 
ening or support, and hence are called mechanical tissues. They 
are also serviceable in conducting the sap. Both in the shape of 
their component cells and in their physiological functions there are 
many transitional forms or gradations between the tissues of the 
parenchymatous and the prosenchymatous groups. The latter 
includes Bast, Libriform, Tracheary and Vascular tissues. 

Bast or Sclerenchyma Fibers. These consist of greatly 
elongated, usually taper-pointed, but sometimes forking or spar- 
ingly branching cells, very thick-walled, tough and flexible. Their 
walls, when mature, are strongly lignified, frequently unequally 
thickened, and often marked with delicate, oblique, slit-like mark- 
ings (Fig. 376). They are usually highly refractive and lustrous. 
Living contents are absent from typical mature bast fibers, in fact 



CHAPTER III. — THE TISSUES. 



195 



the thickening of the walls is frequently so excessive as to almost 
obliterate the cell cavity. 

In longitudinal section, typical bast fibers show their distinctive 
elongated fusiform shape with their tapering ends fitting closely 
together and firmly united (Figs. 376 and 423). In transverse 
section these cells appear as polyhedral plates set in close contact 
with each other so as to resemble a mosaic. 

Bast fibers constitute the tough and stringy tissues in the liber 
or inner bark of Dicotyledons, such as the Bass-wood, Flax and 




Fig. 424. — Portion of transverse section through woody part of stem of 
Pilocarpus pinnatifolius. m, m, medullary ray cells; w, w, wood fibers; d, a 
tracheal tube. 



Leatherwood. The value of Flax for the production of textile 
fabrics depends upon the presence of the fibers. 

Though bast fibers, in the strict sense of the term, are confined 
to the bast or phloem portion of fibro-vascular bundles, fibers 
structurally indistinguishable from them often occur elsewhere in 
the plant. Examples of these are the fibrous tissue that surrounds 
and strengthens some fibro-vascular bundles, as those of Maize 
(Fig. 471); the strengthening cylinder immediately underlying and 
supporting the epidermis of some plants, as that of the stems of 
many Monocotyledons and Ferns ; and the fibrous strengthening 



196 



PART II. — HISTOLOGY. 



cylinder sometimes found imbedded in the parenchyma of stems, 
considerably beneath the epidermis and outside of the fibro-vascu- 
lar bundles, as in the stem of the Pumpkin. The terms "scleren- 
chyma or "sclerenchyma fibers" may, therefore, be applied to all 




Fig. 425. 



tig. 426. 

Fig. 425. — Simple wood 
fibers isolated, showing an 
end and about one-third 
the length of each fiber. 

Fig. 426. — Wood paren- 
chyma cells from Red Oak. 
showing fiber-like form. 



these, and in this sense are used in this work. Fibrous cells, 
unthickened and unlignified and with or without living contents, 
are sometimes associated with the bast. Occasionally these become 
septate. 

Bast is a typical mechanical tissue. It serves to strengthen and 
support the organs in which it is found. It is admirably adapted 



CHAPTER III. — THF TISSUES. 



197 



to this purpose by reason of its ductility and supporting power, 
the latter being comparable to wrought iron. 

Libriform Tissue or Wood Fibers closely resemble bast fibers 
and by some authors are considered as sclerenchymatous fibers, 
along with bast. They differ from bast fibers chiefly as regards 
their position in the plant, for while bast fibers, as has already 
been stated, are located only outside the fibro'-vascular bundle, 





Fig. 427. — Wood parencryma 
cells from Quassia, showing 
pitted markings ; pit. 

Fig. 428. — Transverse section 
of tracheids from White Pine, 
a, is a bordered pit in sectional 



Fig. 427. 

wood fibers are always found constituting a part of the xylem, or 
woody portion of the bundle. As between typical fibers of the 
wood and of the bast, fairly well-marked differences exist, but the 
two grade into one another very closely. From their resemblance 
to bast (or liber) , wood fibers are sometimes termed libriform 
cells. They constitute the great bulk of the wood of most plants 
and abound particularly in the stems of Dicotyledons. The cells 
are compactly arranged, long-fusiform in shape, rarely forked or 
lobed at one or both ends, more or less compressed laterally by 
mutual pressure, so as to appear angular in cross-section, and like 
bast fibers, they are so placed together as to splice one over the 
other, forming a hard and strong tissue, Fig. 424. 

Wood fibers exist in several modifications. The common or 



198 



PART II. — HISTOLOGY. 



typical form is slender-fusiform, thick-walled, with a continuous 
cavity, and the walls sometimes marked with oblique or other 
markings, but frequently without them, Fig. 425. Another form, 
much less common, is distinguished by the possession of transverse 
septa, Fig. 426. 





Fig. 429. 



430. 



Fig. 429.— Longitudinal radial view, showing numerous bordered pits. a, 
a bordered pit ; m, one of a row of medullary ray cells. 

Fig. 430. — Longitudinal tangential section, showing medullary-ray cells and 
tracheids. In this view the pits appear lenticular in shape, and on the margins 
oi the cells, a is one of the pits and jn a medullary-ray cell. 



Tracheids are of elongated tapering forms, therein resem- 
bling wood-fibers, but they are usually of larger caliber and have 
relatively thinner walls, sometimes spirally thickened, sometimes 
marked with various and characteristic sculpturings, thereby re- 
sembling tracheal tubes. In fact, tracheids occupy an intermediate 
position between wood-fibers and tracheal tubes and grade into one 
or the other of these forms very closely. When tracheids occur in 
association with wood cells, as is most commonly the case, they 
are usually larger than these in transverse diameter, and have less 
tapering, merely oblique or even square ends, though there are 
some exceptions to these rules. When arranged end to end in 
linear series, they are indistinguishable from tracheal tubes, save 
by the imperforate transverse or oblique partitions. 

In the Pines and related plants a peculiar kind of tracheid com- 
poses the wood, giving to coniferous woods peculiarities which 
enable us to readily recognize them. If a radial section of the 



CHAPTER III. — THE TISSUES. 



199 



wood of the common White Pine be made, the elongated, fusiform 
cells of the woody zone will be seen to possess numerous rounded 
pits, each of which, in this view, looks like two circles, one within 
the other. They occur mostly on the radial walls of the cells, as 




Fig. 431. — Diagrammatic representation of a block of pine wood, highly 
magnified, a, early growth; b, late growth; c, intercellular space; d, bordered 
pit in tangential wall of late growth ; m, f and e, bordered pit in radial wall of 
early growth from different points of view ; h, row of medullary cells for carry- 
ing food; g, row of medullary ray cells for carrying water; k, thin place in 
radial wall of ray cells that carry food. (Stevens.) 



is shown by comparing the radial, transverse and tangential sec- 
tions. The comparison will also show us that the bordered pits, 
as they are called, are lenticular areas in the common wall between 



200 



PART II. HISTOLOGY. 



two adjacent cells. These areas have their lateral walls perforated 
centrally with a circular or oblong perforation. It is this which, 
in the radial view, gives rise to the optical impression of an inner 
circle in each pit. The perforation, however, does not extend, 



Fig. 432. 




Fig. 433. 



Fig. 434. 



Fig. 435. 



Fig. 436. 



Fig. 432. — A dotted or pitted tracheal tube from Milk-weed. 
Fig. 433. — Part of a scalariform tracheal tube from a fern. 
Fig. 434. — Spiral tracheal tubes ; a, one with a single spiral band ; b, one with 
triple spiral. 

Fig. 435. — An annular tracheal tube from house Geranium. 
Fig. 436. — A reticulate tracheal tube from house Geranium. 



except in very old wood, completely through the common wall from 
one cell to the other, but there still remains stretched across the 
cavity of each area a delicate separating membrane. The structure 
will be understood by references to Figs. 428, 429 and 430, which 
represent small portions, respectively, of transverse, radial and 
tangential sections of White Pine wood, and Fig. 431, which is a 



CIIAITER III. THE TISSUES. 



201 



diagrammatic representation of Pine wood showing the cellular 
structure in three dimensions. 

The parenchyma cells, with bordered pits, which occur imme- 
diately within the bundle sheath in the leaves of Pines, may be 
regarded as transition forms between ordinary parenchyma and 
the tracheids just described. Indeed, by -some they are classed as 
tracheids. 




Fig. 437. 

Fig. 437. — Transverse view of trabecular tracheids 
from leaf of common Juniper ; p, a bordered pit ; a, 
thickening crossing the lumen of the cell. 

Fig. 438. — Longitudinal view of the same, magnified 
to the same extent. The letters also refer to the same 
structures. 




Fig. 438. 



Just as wood fibers grade into vessels they also, on the other 
hand, approach parenchyma, and we frequently find among the 
woody tissues rows of rather thin-walled cells, like those repre- 
sented in Fig. 427, the end ones taper-pointed, the middle ones 
blunt-ended, and together forming a combination shaped like a 
wood cell. Such tissue is termed ivood parenchyma, and the name 
happily expresses its intermediate character. 

Vascular Tissue. These cells, variously known as ducts, tracheal 
tubes or vessels, differ from tracheids mainly in being composed 
of two or more cells which have become confluent end to end, 
forming tubes of varying length. Their diameter is commonly 
large, compared with that of the other wood cells of the same 
plant, and they are usually much longer. When mature, their 
walls are lignified, their lumen commonly filled with air, though 
sometimes with cell-sap, and they are destitute of cytoplasm. The 



202 PART II. — HISTOLOGY. 

thickenings, which constitute the markings, are on the internal 
surface of the wall, and the different kinds of tracheal tubes are 
named from the character of these markings. 

The following kinds are the most" important : 

The Potted or pitted are characterized by rounded or oblong, 
thin areas or pits scattered over the wall, as in Figs. 432 and 440. 




Fig. 439. — Transverse section of the wood of Vitis vinifera, showing large 
vessel filled with old tyloses. At the left a young tylose growii g out of a wood 
parenchyma cell. (After Reess.) 

The Scalariform differs from the dotted chiefly in the fact that 
the pits are greatly elongated in a transverse direction, giving rise 
to markings which bear some resemblance to the rounds and spaces 
of a ladder ; hence the name ; Fig. 433. 

The Spiral are those in which the markings consist of spiral 
thickenings. The spirals may be loosely or compactly arranged; 
they may be single, double, treble, or even sextuple. The rest of 
the wall on which they are borne is usually thin, so thin that when 
a stem or other organ containing them is torn asunder by a longi- 



CHAPTER III. — THE TISSUES. 



203 



tudinal strain, the cell-wall is ruptured, and the spirals are drawn 
out, sometimes to great length, and appear to the naked eye like 
spider lines. Two of these tubes are shown in Fig 434, a and b. 

The Annular are those in which the thickenings take the form 
of rings, Figs. 377 and 435. Transition forms between these and 
spiral vessels are often met with. For example, one end of the 
tube may possess a spiral, while the other is annulate. 

The Reticulate vessel is one in which the thickenings take the 
form of a reticulum or network, as in Figs. 375 and 436. Interme- 
diate forms between this and the spiral are also sometimes seen, 
and gradations occur between this and the dotted vessel. 

The Trabecular is a rarer form, in which the thickenings cross 
the lumen of the cell. On either side of the central fibro-vascular 




Fig. 440. — Quassia wood, showing the structure, a, wood fibers ; b, tracheal 
tubes ; c, medullary rays ; d, wood parenchyma, bearing prismatic crystals of 
calcium oxalate. 



bundle in the leaf of the common Juniper occur tracheids having 
thickenings of this character. Fig. 437 represents some of them 
as they appear in transverse section, and Fig. 438 some of the 
same in longitudinal view. 



:o4 



PART II. — HISTOLOGY. 



Occasionally parenchyma cells lying alongside the tracheal 
tubes, force their way through the thin places in the walls of the 
tubes and more or less completely fill the cavity. These are termed 
tyloses (see Fig. 439). 

In wood fibers the mechanical function predominates and the 
conducting work is secondary, but with tracheids and tracheal 
tubes the reverse is true. Tracheary cells serve only incidentally 
to support the plant, their prime purpose being to convey water 




Fig. 442. 



Fig. 441. — Phloem tissue from Pumpkin stem, showing, a. e and f, 
plates ; b, companion cell ; c, parenchyma cell in transverse secron. 

Fig. 442. — Phloem tissue from Corn stem, showing, a, sieve plate ; b, 
panion cell, and d, zylem. 



and watery sap, while the conduction and storing of the elaborated 
foods are carried on chiefly by the parenchyma cells. Fig. 440 
shows the relation of wood fibers, tracheal tubes, and wood paren- 
chyma to the medullary rays in Quassia wood. 

Conducting tissues, both woody and parenchymatous, are some- 
times grouped as Mestome. 

Sieve Tissue. This includes the different varieties of Sieve 
Cells, which are the essential feature of the phloem of fibro-vascu- 
lar bundles. They consist usually of elongated, thin-walled and 
blunt or somewhat oblique-ended, relatively large cells, arranged 
in longitudinal rows and having areas with sieve-like perforations, 
technically called sieve-plates, on some portion of their surface. 
Accompanying them may be elongated parenchyma cells, with liv- 



CHAPTER III. — THE TISSUES. 



205 



ing contents known as companion cells. The sieve and companion 
cells, with parenchymatous elements (cambiform cells or lep tome- 
parenchyma) that may also be present, constitute the phloem 
(lep tome) of the vascular bundles (mestome strands). 

In some forms of this tissue, as in the stem of the Pumpkin, 
where it is abundant and well developed, the ends of the cells, and 
not the sides, have the most prominent sieve plates. Figs. 441, 
442 and 443. In others the plates are more prominent on the side 
walls than on the end partitions, but not infrequently they occur 
on both, as may be seen in some of the sieve-cells of the Pumpkin. 



P — 



n 




i 






■ 


jy 


t\ 


1 ■» 





/'< 


a " 






to \ 




Fig. 444. 

Fig. 444. — a, row of latex cells from rhizomes 
of Sanguinaria ; b, portion of latex tube, com- 
posed of several confluent latex cells from the 
same plant. 

Fig. 443. — Longitudinal view of sieve tissue 
from Pumpkin, s, a sieve-cell ; p, a thickened 
sieve-plate ; attached to either surface of the 
sieve-plate are masses of albuminoid matter, a. 
shrunken by treatment with alcohol ; c, com- 
panion cell. 



Fig. 443. 

Mature sieve-tubes usually contain a thick, slimy, albuminous fluid 
composed partly of the cytoplasm lining the tube and partly of 
watery or somewhat mucilaginous material. When the sieve tubes 
are cut and exposed to air or when they are treated with strong 
alcohol this fluid coagulates and is then most abundant and dense 
next to the transverse plates, as shown in Fig. 443, which repre- 
sents a longitudinal view of sieve-tissue from the Pumpkin stem 



206 PART II. — HISTOLOGY. 

after having been treated with alcohol. In places the albuminoid 
matter is shrunken away from the sieve-plate. From mature 
sieve tubes the nucleus has disappeared; the cytoplasmic filaments 
are continuous from one cell to the next through the perforations 
in the plates; thus the protoplasts are connected, forming an 
organic whole, and the sieve cells, during the growing season, at 
least, form long, continuous tubes, through which nutritive mate- 




Fig. 445. — Branched latex vessel from Euphorbia splendens, containing 
bone-shaped starch grains embedded in the latex. 

rials circulate in the plant. The sieve-plates are usually much 
thickened, often with a deposit of a peculiar lustrous, gelatinous 
character called callus, which may line the pores only or may 
cover the whole plate. The rest of the cell-wall remains very thin 
and is composed of unmodified cellulose. The function of this tissue 
is, presumably, the distribution of nitrogenous food substances 
through the plant. The non-nitrogenous foods, carbyhydrates 
especially, are apparently conveyed by the sap. 

Secretory tissues serve the special function of forming and 
storing secretions. By the term "secretion" as used in this con- 
nection is meant those substances formed during the life of the 
plant which are not, so far as we know, used by the plant as food, 
nor in the construction of the cell-walls. Such secretions include 



CHAPTER III. — THE TISSUES. 



207 



the volatile oils, resins and balsams, and a variety of other sub- 
stances. The latex or milk-juice of plants, while containing food 
substances, consists largely of waste products, and is therefore 
included here. 




Fig. 446. — Laticiferous vessels from the bark of the root of Scorozonora his 
panica; a, as seen under low power, and, b, under high power. ("After Sachs.)- 

The substances above mentioned may occur in plants in spe- 
cially modified cells, as the glandular trichomes already noticed ; in 
tubes or sacs, which may be either single cells or formed from 
rows or groups of cells which have become confluent through the 
breaking away of their walls (see Figs. 444 and 445), as in many 



208 



PART II. — HISTOLOGY. 



rnilk- vessels and resin receptacles; and in passages formed by the 
splitting apart of cells (intercellular spaces), as in many oil- 
glands, resin and balsam passages. Such intercellular passages 




Fig. 447. — Latex tubes from the cortex of Dandelion root, under high 
magnification. 




Fig. 448. — Section of the cortex of Ginger, showing okoresin sacs. a. 
oleoresin sac ; b, intercellular space ; c, parenchyma cell. 



CHATTER III. — THE TISSUES 



209 



arc usually surrounded by a layer of secreting cells, which secrete 
the contents of the passage or receptacle. 

Many plants, when wounded, emit a milky fluid, varying in 
color, copiousness, consistency and chemical composition in differ- 




Fig. 449. — Oleoresin glands in Male Fern rhizome. a, stalked oleoresin 
gland ; b, intercellular space ; c, parenchyma cell. 

ent plants. The vessels which contain this fluid, or latex, are 
called laticiferous vessels and may occur in any organ of the plant. 




Fig. 450. — Mucilage sacs of Elm bark, transverse section ; a, mucilage sac ; 
b, bast bundles; c, medullary ray. 

Three kinds are distinguished — the simple short cells (Fig. 444) ; 
tubes which consist of single, greatly elongated, and usually 



210 



PART II. — HISTOLOGY. 



branching cells, which originate in the growing tissue and follow 
the extension and branching of the organ in which they occur, as 
in the Euphorbias and Asclepiads (Fig. 445) ; and vessels which 
consist of coalesced cells, forming an irregular network, as in the 
Dandelion and other Cichoracese (Figs. 446 and 447). The latex 
cells have cellulose Walls which are smooth and elastic. They are 
living cells with cytoplasm and nuclei lining the inner surface of 
their walls. 



SSM 1 






Fig. 451. 



Fig. 451. — Schizogenic mucilage passage 
from the stem of Rhamnus Purshiana. 

Fig. 452. — Formation of a lysigenous 
gland in the leaf of Fraxinella. A and B. 
early stages of development ; c, a mature 
gland containing a large drop of secreted 
oil. (Sachs.) 



Fig. 452. 
Secretory Cells are for the most part slightly modified paren- 
chyma cells, rather seldom suberized, and known under the general 
name of "secretory sacs." The oleoresin sacs of many spices, such 
as Ginger (Fig. 448) and Pepper, the volatile oil cells of the Star 
Anise and the peculiar internal glands of Male Fern rhizome (Fig. 
449) are examples of secretory cells. It is convenient to classify 
them according to their contents. Thus some contain crystals, 
and are called crystal cells; in many of these the protoplasmic and 
other contents have almost, if not completely, disappeared, and the 



CHAPTER III. — THE TISSUES. 



211 



cell is nearly or quite filled with the crystals (Fig. 359). Other 
cells, on account of their resinous or balsamic contents, are called 




Fig. 453. — Cross-section through a portion of orange peel, showing the cav- 
ity of an interior, globular gland at (g) ; crystals of hesperid ; n at (h) ; calcium 
oxalate crystals at (k). (Tschirch and Oesterle.) 




Fig. 454. — Resin canals in the young stem of the Ivy (transverse section). 
A, B, C, young canals (g) at the boundary of the cambium (c) and soft bast 
(wb) ; h, wood. D and E, larger and older canals (g) lying at th; boundary 
between the bast (b) and the cortical parenchyma (rp). (Sachs.) 



212 



PART II. — HISTOLOGY. 



resin sacs; others, containing mainly tannin, are called tannin 
sacs; still others that contain volatile oil are termed oil sacs; and 
those that contain an abundance of mucilaginous or gummy mat- 
ter are named mucilage sacs (Fig. 450). 

Secretory Passages may be either intercellular spaces or canals 
formed by the fusion of rows of cells. They may contain volatile 
oils, oleoresins, balsams, mucilage or other secretions and are 




Fig. 455. — Glandular hair from leaf of House Geranium, showing a single- 
celled gland ; a, stalk of the hair ; z, secretory cell ; s, secretion cavity of the 
cuticle formed by distension. (Haberlandt.) 



formed in different ways; sometimes by the splitting of the com- 
mon cell- wall which separates adjacent cells, a mode of formation 
described by the term schizogenous (Figs. 451 and 454) ; sometimes 
by the rupture and destruction of certain cells, a process described 
as lysigenous (Figs. 452 and 453). In some instances, passages 
originate in a schizogenous manner but their later development is 
lysigenous. The oil tubes characteristic of the umbelliferous 
fruits, Anise, Fennel and Caraway, and the oleoresin passages of 
the Pine trees, from which we obtain Turpentine, are examples of 
secretory passages (Fig. 454). 

Glandular hairs consist essentially of a secretory gland borne 
upon a stalk of varying length. The gland may be one-celled ( Fig. 
455) or several celled (Fig. 456). (Refer also to Figs. 411 and 
416.) In glands which secrete volatile oil or resin, the secretion 
originates in the cell-wall, appearing between the cellulose layer 
and the cuticle, and finally breaks through the latter and escapes. 
Related are the nectaries which secrete the sugary nectar that 



CHAPTER III. THE TISSUES. 



213 



serves to attract insects to flowers, the digestive glands of insectiv- 
orous plants, and the mucilage hairs or "colleters" on many leaf 
buds. 



QQQQC: 




Fig. 456.— Glandular hair from leaf of Peppermint, showing a many-celled 
gland; a, short stalk; b, secretion cells; c, much distended; s, secretion cavity. 



Practical Exercises. 



1. For the study of meristematic tissue, examine sections cut lengthwise 
through the embryo of a grain of corn and which have been prepared by staining 
with rosanilin and mounting in balsam. The cells are rectangular in shape, 
nearly isodiametric and average about fifteen microns in diameter. The nucleus 
is stained more deeply than the surrounding cytoplasm and the cell-wall is very 
thin and delicate. 

Compare the sections of the onion root tip properly fixed, stained and 
mounted. (See Fig. 333.) 

2. For the study of parenchyma examine a transverse section of the rhizome 
of May Apple (Podophyllum peltatum). This is a dicotyledonous stem and 
exhibits a large central pith surrounded by about sixteen or more small wood- 
wedges separated by broad medullary rays, and outside of the woo 1 a rather thick 
bark. The pith, medullary rays and middle bark consist of parenchyma tissue. 
With the low power observe the shape and comparative size of the cells of these 
parts and the nature of their cell contents. Cellulose walls are indicated by the 
purple color with zinc chloriodide and liquefied walls by the cherry red color 
with phloroglucin solution. In a similar manner study a longitudinal section of 
the rhizome and make a drawing. 

3. From a stem or petiole of the Pickerel Weed (Pontederia cordata) remove 
one of the membrane-like plates which are found extending across the large air 
passages. Under the microscope this plate will be seen to consist of stellately- 
shaped parenchyma cells, joined together by the projecting ends of neighboring 
cells and having intercellular spaces in the angles. Notice that attached to or 
suspended from this tissue are oval cells containing raphides and globular cells 
filled with a brown resin. 

4. For the study of collenchyma examine a transverse section of the 
petiole of the Yellow Dock (Rumex crispus). Mount in Water and view with 
the low power. Notice that the outer side of the petiole is ribbed. Underlying 



214 PART II. — HISTOLOGY. 



the epidermis at each of these ribs is collenchyma tissue. Compare the appear- 
ance of the collenchyma cells with the description given in the text. Test with 
iodine solution and notice whether cell-contents are present. With the high 
power examine the cell-walls and notice whether stratifications are visible. Apply 
the zinc-chloriodide test for cellulose. 

Examine a longitudinal section and state how the length of these cells 
compares with their breadth. 

Excellent examples of collenchyma tissue are also afforded by the petioles 
of the Burdock, Pie Plant, Grape or Begonia. 

5. For the study of sclerotic tissue make a scraping of the flesh of the Pear 
(Pyrus communis) and mount in water. View with the low power. Little 
bunches of grayish, thick-walled cells will be found imbedded in the soft, thin- 
walled parenchyma cells of the fleshy part. Rather firm pressure with the point 
of a knife is required to break up these groups into their component cells. Apply 
the phloroglucin test. The walls of the sclerotic cells are colored red. Notice 
the great thickness of the wall and the small lumen of these cells. Simple and 
branched pores extend from the lumen through the wall. 

For a tissue consisting entirely of sclerotic cells examine the shell of the 
Coconut (Cocos nucifera), taking two sections, one tangential and one radial 
to the surface of the shell. 

7. Make thin sections of the shell of a Hickory nut, some of them parallel 
with the surface, and others at right angles to it ; treat the sections with hot 
Schulze's fluid ; rinse, stain with methyl-green, mount in water, and jar the cells 
apart by tapping the cover-glass with a needle ; then study the cells with the 
high power. Observe the excessively thickened walls, and the concentric and 
radial markings. 

8. The sclerotic cells of the Tea Leaf (Thea sinensis) are striking and 
characteristic. They occur imbedded in the parenchyma tissues adjacent to the 
midrib, and may be seen to good advantage in a transverse section of the leaf, 
especially when the latter is stained with phloroglucin solution. Examine such a 
section, stain as indicated, and draw one or more of the peculiar sclerotic cells. 

9. With the forceps remove a small piece of the epidermis, or with a razor 
cut a surface section including only the epidermis from the under side of a leaf 
of the Tulip (Tulipa gesneriana). Mount the specimen in water and view first 
with the low, then with the high power. Notice the shape and arrangement and 
contents of the epidermal cells. Observe the stomata and note how these differ 
in size and shape from the other epidermal cells. Notice that the guard-cells ot 
the stomata are the only epidermal cells which contain chlorophyll. 

10. For a sectional view of the epidermis, study a transverse section of the 
leaf of the Tulip. Notice particularly the shape of the epidermal cells, the 
thickness of the cuticle, the location of the stomata and the nature of the open- 
ing between the guard-cells. Notice that the stomata never occur above a vein, 
but only where the underlying parenchyma cells are loosely arranged, and that 
beneath each stoma is an intercellular space. 

11. Examine in the same manner a surface section from the lower face of 
the Stramonium leaf (Datura stramonium). Compare the arrangement of the 
epidermal cells and stomata in this, a dicotyl leaf, with that of the tulip, a 
monocotyl. Notice the altered form of the epidermal cells and the absence of 
stomata where the epidermis overlies a vein of the leaf. Compare a similar 
section from the upper surface of the leaf. In which section are the stomata 
more numerous? 

12. Examine a transverse section of a young stem of Velvet Leaf (Abutilon 
avicennae). Notice the two kinds of trichomes present. Determine the charac- 
ter of the cell-walls and contents of each, applying appropriate tests. Notice 
the relation between the plant-hairs and the ordinary epidermal cells. 

13. Compare the plant-hairs of the Mullein leaf (Verbascum thapsus), exam- 
ining in the same manner. 

Mount a few hairs of absorbent cotton. Notice the ribbon-like appearance 
and the characteristic spiral twisting of the collapsed plant-hairs. Observe that 
each of these hairs is composed of but a single cell. Apply the test for cellulose. 

14. Study the cork cells of the stem of the Elder (Sambucus canadensis) in 
transverse and longitudinal sections. Notice the shape and arrangement of these 
cells and especially the cell-contents in the phellogen layer after testing with 
iodine solution. Describe the thickness and color of the walls. Test for wall- 
substance. 

Study sections of a bottle cork (Quercus suber), cut radially, tangentially 
and transversely. Refer to Fig. 379. Notice that the cells are not of uniform 
size, but that the large, rather thin-walled, cubical cells pass into flatter cells, 
giving the appearance of a dark zone, which, like the annual rings in woods, 
marks the limit of a year's growth. Treat the section with potassium hydrate 



CHAPTER III. — THE TISSUES. 215 



solution and warm the slide. How are the cell-walls affected? In a similar 
manner examine the cork cells of the Potato (Solanum tuberosum), and of Red 
Cinchona Bark (Cinchona succirubra). 

15. For the study of typical bast fibers, examine transverse and longi- 
tudinal sections of the stem of the Sunflower (Helianthus annuus). The bast 
layer is located in the inner bark and the fibers are grouped into crescent- 
shaped bundles, which lie opposite and outside the wood-wedges. Apply the 
phloroglucin test. Describe the individual fibers as to shape, thickness of wall 
and markings. Notice also the relative size of the. cell-cavity. In a longitudinal 
section observe the shape of the bast fibers and the manner in which their ends 
overlap. Compare fibers obtained by macerating the bark in Schultze's fluid. 
In a similar manner study transverse and longitudinal sections of Cinchona bark, 
and notice how these bast fibers differ from the preceding in size, shape, mark- 
ings and relative arrangement. 

16. Compare the textile fibers of Flax, Hemp, Jute and Ramie with the 
trichomes constituting cotton, the hairs of wool and the threads of silk. 

17. For libriform tissue examine a transverse section of the root of Gel- 
semium sempervirens, staining with phloroglucin. The walls of the cells com- 
posing the woody zone are stained re"d, indicating that these membranes are 
lignified. 

Observe that these cells are of various sizes and forms. Those with a large 
rounded cavity and thin walls are the tracheal tubes. The smaller and more 
nearly square cells with relatively much thicker walls, which form a tissue filling 
in between the tubes, are the wood fibers, while extending through these in 
radial rows of one to six cells in width are the medullary rays, composed of 
tabular, radially extended and lignified parenchyma cells. In a longitudinal sec- 
tion stained with the phloroglucin reagent observe the shape of the wood fibers, 
their relative arrangement, and the oblique slit-like markings on their walls. 

18. In a similar manner study the Quassia wood (Picrasma excelsa), staining 
with iodine. The fibers are stained brown, the medullary rays yellow and the 
starchy contents of the wood-parenchyma are stained black. Compare tangential 
and radial sections of the latter as regards the position and appearance of the 
medullary rays. 

19. For the study of tracheids examine a radial section of Pine wood, stain- 
ing with phloroglucin. Observe that the section is entirely composed of tracheids 
except where these are crossed by medullary rays. The tracheids are of typical 
shape and are marked by one or two rows of pitted markings, each of which 
appears as of two concentric circles. Within the inner circle is the thinnest 
portion of the wall, consisting of a delicate membrane, unequally thickened and 
partly lignified, forming the bottom of the so-called "pit." The portion between 
the circles is the wall of the pit, while the cell wall beyond shows the maximum 
thickening. The pits are, then, thin places in the wall, and each might be com- 
pared with a very wide-angled funnel, having the neck removed, and the larger 
opening closed by a membrane. In contiguous cells the pits are directly 
opposite, so as to resemble two such truncated funnels placed top to top, with 
only a diaphragm between. In the older cells this separating membrane is fre- 
quently absent. 

Compare a tangential section. Notice that the markings upon the tracheids 
appear disk-like and only on the lateral walls, while the under or upper walls are 
rarely so marked. Observe that the medullary rays in this section appear as 
short fusiform groups of cells lying between the tracheids. 

Take next a transverse section. In this view the tracheids appear roundish 
or nearly square in form. The appearance of the pits resembles that in the 
tangential section, but they are few and difficult of observation Notice that the 
tracheids are arranged in radial rows constituting the wood wedges, these being 
separated by medullary rays. Annual rings are distinctly visible in this sec- 
tion. These rings are made evident by the contrast caused by the small, thick- 
walled cells of the fall growth, being immediately succeeded by the much larger 
and thinner-walled cells formed during the following spring. 

20. In the preceding studies we have had occasion to observe the shape of 
the tracheal tubes in both transverse and longitudinal section. For a study of 
the characteristic markings upon their walls examine the fo'iowing: Corn (Zea 
mays) stem— pitted, annular and spiral markings. Brake Fern (Pteris aquilina) 
rhizome — scalariform markings. Podophyllum rhizome — reticulate markings. 

21. For the study of sieve tissue examine a transverse section of the stem 
of the Pumpkin (Cucurbita pepo). Stain with phloroglucin solution. Notice 
the presence of large tracheal tubes in the xylem. On either side of the xylem 
layer is located a crescent-shaped phloem mass. Th two phloem strands curve 
around the xylem until they almost encircle it. Stain another section with eosin 
or with methyl blue. If the latter stain is used, mount the specimen in glycerine. 
The albuminous contents of the sieve tubes are stained blue and the plates are 



216 TART II. — HISTOLOGY. 



distinctly seen. Many of the sieve tubes display no plates for the reason that 
the section has been made above or below the plane in which the plates of these 
cells were located. The companion cells are here much smaller than the sieve 
tubes. Compare longitudinal sections similarly stained, where plates can be 
observed on the lateral walls. 

22. Examine a longitudinal section of the fruit of Osage Orange (Toxylon 
pomiferum). In the parenchyma are located many latex-tubes, which the 
coagulated and yellow-colored milk-juice renders distinctly visible. The tubes 
consists of elongated, simple or branched cells. 

23. In a similar manner study the milk-vessels of Dandelion (Taraxacum 
officinale) as displayed in the bark of the root. The vessels in this root are 
formed through fusion of rows of cells and are branched, the branches anasto- 
mosing freely. 

24. Study the mucilage sacs of Althea root (Althea officinalis), mounting 
the sections in glycerine and alcohol. Test with zinc chloriodide. Compare sec- 
tions of Slippery Elm bark (Ulmus fulva). 

25. Make a study of the resin-passages of the root of the American Spike- 
nard (Aralia racemosa), examining transverse and longitudinal sections. These 
passages occur in the bark parenchyma and each passage consists of an inter- 
cellular space surrounded by secreting cells. 



CHAPTER IV.— THE HISTOLOGY OF THE ORGANS. 

The Root. — The growth in length of roots is accomplished by a 
meristem located near the apex of the plant organ. This tender 
growing-point is protected by the root cap — a covering of loose, 
parenchyma tissue. Such a meristem is composed of embryonic 
tissue, the cells of which are capable of dividing rapidly and in all 
three planes of growth — radial, tangential and transverse. These 
cells are polygonal in shape with thin cellulose walls, and are filled 
with cytoplasm and contain relativly large nuclei. This is the 
primordial meristem. A short distance back from the growing 
point, it is differentiated into three parts, known as primary meri- 
stems, from which the primary permanent tissues are developed 
(Fig. 458). From the outermost of these, the protoderm, the epi- 
dermis is developed. In the younger portion of the root the 
epidermis is characterized by bearing numerous blunt, single-celled 
and thin-walled root-hairs, through which the plant obtains its 
supply of water and nutritive substances from the soil. As the 
root lengthens the older hairs die off and new hairs arise from 
the epidermis lower down toward the apex. A cuticle is lacking 
from this youngest portion, but as we pass further backward, we 
find that the epidermis of the older part of the root is strongly 
cutinized and is frequently reinforced by one or more layers of 
cells comprising the hypodermis. 

The second of the primary meristems is the middle layer and 
is called the periblem. From this originates the primary cortex — 
composed usually of parenchyma and extending from the epidermis 



CHAPTER IV. — THE HISTOLOGY OF THE ORGANS. 



217 



on the outside to the endodermis on the inside. The third primary 
meristem is located at the centre and is called the plerome. It 
gives rise to the stele or central cylinder, which is surrounded by 
a sheath of a single layer of compactly-arranged cells somewhat 
flattened in a radial direction, often suberized or lignified and 




Fig. 458. — Longitudinal section through the root apex of Corn. a, older 
portion of root-cap ; i, younger part of same ; s, apex of growing-part ; e, ex- 
ternal layer of tissue of root — the cell-walls are thickened (v) ; r, young cor- 
tex; f, cells of axial vascular bundle; g, flattened cells of a large vessel, which 
will subsequently form long cylindrical segments with bordered pits ; m, paren- 
chyma of the pith in the axial strand (highly magnified). (Sachs.) 



218 



PART II. — HISTOLOGY. 



constituting the endodermis or starch sheath. The stele consists 
of mestome strands of tracheal tubes and sieve tissue, known as 
hadrome (xylem) and leptome (phloem) , respectively, which are 
imbedded in fundamental tissue forming what is called a radial 
vascular bundle. 




Fig. 459. — Two-rayed vascular Lunelle from a young root of Podophyllum. 
1, endodermis; 2, phloem tissue; 3, tracheal tube of the xylem; 4, cortical 
parenchyma. 



The structure above outlined, having developed from the pri- 
mary meristems, is called the primary structure (Figs. 458, 459 
and 460). 

The roots of Club-mosses, Ferns and nearly all Monocotyledons 
conform in a general way to this description and undergo little- 
change with age, excepting the cutinization or lignification of cer- 
tain tissues. The roots of Dicotyledons and Gymnosperms, how- 



CHAPTER IV. — THE HISTOLOGY OF THE ORGANS. 219 

ever, may have a later growth in thickness, due to the development 
of secondary meristems and giving rise to a secondary structure 
(Fig. 463). 

One of these secondary meristems is the phellogen, or cork- 
cambium, which develops in the cortex just beneath the epidermis, 
or at times in the epidermis itself, and through division of the 
cells in tangential and radial directions produces a layer of cork. 
Since the walls of the cork cells are suberized and impervious to 
water, the sap supply of the epidermis and sometimes of the pri- 
mary cortex is cut off and these tissues gradually die and are 




pc — 



^ Fig. 460. — Radial vascular bundle from Calamus root; s, endodermis ; 
pc, procambium ; ph, phloem strand; g, xvlem rav ; m. cc-itral parenchyma. 
(Sachs.) 

thrown off, leaving the cork as a permanent protective covering 
for the root. 

The other secondary meristem is the cambium, which develops 
from procambium cells situated between the primary xylem and 
the primary phloem and produces the most striking changes in the 
structure of the root. On the inner face of these cambium strands 
not only new tracheal tubes, but also tracheids, wood fibers and 
wood- parenchyma may form, giving rise to a xylem of more com- 
plex composition, the secondary xylem. The activity of the cam- 



220 



PART II. — HISTOLOGY. 



bium is mostly on the xylem side so that the xylem increases in 
thickness and pushes out the phloem until the xylem has assumed 
a cylindrical form and is separated from the surrounding cylinder 
of phloem by the layer of cambium that lies between. Strips of 
parenchyma tissue, the cells of which are more or less flattened 
and are elongated in a radial direction, divide the xylem into 
wedge-shaped portions. These parenchyma rays are formed at 
the cambium. They are called medullary rays. Thus, when the 
secondary structure is completed, the original radial vascular 
bundle of the stele has been changed into a circle of open collateral 
bundles, each consisting of a xylem and phloem strand with a 





"jT 






im m 




m;. 



Fig. 461. — Transverse section of the root of Blue Flag (photo-micrograph), 
ep, epidermis, with an occasional, nearly obliterated root-hair; hp, bypodermis 
of two or three rows of rather thick-walled cells; c, cortex of loosely arranged 
parenchyma ; en, endodermis ; ph, phloem strand ; x, xylem ray. 

cambium between and in that sense "open" to further growth in 
thickness. These wood bundles are separated by medullary rays. 
The cambium crosses these rays, forming a complete circle. As 
growth proceeds annual rings may form in a manner to be ex- 
plained under stem structure. 

The growth from the outer face of the cambium develops not 



CHAPTER IV. — THE HISTOLOGY OF THE ORGANS. 



221 



only new sieve tissue, but also bast fibers, medullary rays and 
occasionally sclerotic cells. In the course of this growth the tissues 
of the cortex and the epidermis are replaced by cork and secondary 
parenchyma. As a result, we have a complete bark, replacing the 
original cortex. Meanwhile, the endodermis has disappeared. A 
pith is absent from the root except near where the root and stem 
join. 

Branches of the root originate from the cells of the pericycle 
situated just within the endodermis; the rootlets extend outward 
through the cortex, being assisted by the digestive action of an 
enzyme. Each develops its own root cap and corresponds in struc- 
ture with the parent root. 

The roots of vascular cryptograms, except Lycopodiacese, differ 
from those of flowering-plants in the fact that they increase in 
length by the division of a single sub-apical cell instead of a mass 




Fig. 462. — Large radial fibro-vascular bundles from Sarsaparilla rcot (photo- 
micrograph), c. small portion of cortex; e. endodermis; ph. phloem strand; 
x, xylem rays; m. central parenchyma. 



222 



PART II. HISTOLOGY. 



of such cells. The roots of Lycopodiacem differ from those of 
Ferns and flowering-plants in the fact that their mode of branching- 
is dichotomous. In the higher plants and in Ferns root-branches 
always originate as lateral outgrowths. 




Fig. 463. — Transverse section of the root of Black Indian Hemp (Apocynum 
cannabinum), (photo-micrograph), showing the secondary development of a 
root, ck, cork ; pi, phellogen or cork cambium ; mb, middle bark ; ib, inner 
bark, including the phloem ; c, cambium ; sc, secondary wood of several years 
growth ; pri, primary wood, represented by a minute star at the center. 

Plants below vascular cryptogams do not possess true roots, 
but many of them produce outgrowths of much simpler structure, 
destitute of vascular tissues, which serve the purpose of securing 
the plants to the soil or rocks. Such organs are called rhizoids. 

The Stem. — The stem originates in a primordial meristem which 
displays the same structure and develops the primary meristems 
as does that of the root. However, a cap is lacking, the primordial 
meristem being located at the apex, though the region of growth 
may extend back through several internodes (Fig. 464). 

Primary structure. — Except for the presence of stomata and 



CHAPTER IV. — THE HISTOLOGY OF THE ORGANS. 



223 



the variety of its trichomes, the epidermis of the stem differs little 
from that of the root. In herbaceous plants the epidermis is 
commonly persistent, while in woody-stemmed plants it is usually 




V 



Phlpen.fron.^ro^b^tlnd'caSMun,^ phloem from Vhe procamMu. .nd cambiu- 

Fig. 464. — Diagram, showing the evolution of tissues from the primordial 
meristem down to the beginning of cambial activity. In the longitudinal dia- 
gram, at the bottom, the initial C of the work cambium stands directly be- 
neath this tissue, which is radially but one cell in thickness. (Stevens.) 

replaced by cork. The primary cortex here resembles that of roots 
save that the stem-cortex may comprise chlorophyll-bearing cells 
and that its tissues are usually more varied and complex than are 
those of the corresponding portion of the root, thus collenchyma 
is commonly present and serves to strengthen the young stem 



224 



PART II. — HISTOLOGY. 



until the development of bast and xylem. Sclerotic cells are also 
frequently met with. 

The endodermis, which jnarks the inner boundary of the cor- 
tex, is composed of cells rich in starch and known as the starch 
sheath. 

All the tissues within the starch sheath are included in the 
stele. 

The pericycle, or outer part of the stele, may contain bast 
fibers, either forming a continuous ring or in separate groups or 




Fig. 465. — Transverse section of the rhizome of Brake Fern (photo-micro- 
graph), a. one of the several lepto-centric bundles; b, sclercnchyina strand; 
c, suberized parenchyma ; d. starch-bearing parenchyma. 

strands. Associated with these, sclerotic cells are often found. 
Bast and sclerotic together constitute the stereome. 

Within the pericycle are the vascular bundles (mestome 
strands), their structure and arrangement being characteristic of 
the principal kinds of stems, namely Ferns, Monocotyledons and 
Dicotyledons. 

The Fern Type. In the Ferns and their allies, the bundles 



CHAPTER IV. — THE HISTOLOGY OF THE ORGANS. 



225 



(mestomc) are usually of the concentric (hadrocentric) variety, 
consisting of xylem (hadrome) surrounded by phloem (leptome) 
associated with more or less parenchyma tissue and surrounded 
by an endodermis. In some cases there may occur within the stele 
but a single bundle, from which branches are given off to the 
leaves; in others, there may be two or more bundles placed side 
by side; and in still others, and this is the commonest arrangement, 
they are disposed in a single circle. But when distributed circu- 
larly, they are never radially elongated, as are the bundles in the 
stems of Dicotyledons, and if viewed in transverse section they 
appear either circular, or more or less lengthened in a tangential 
direction. In the smaller strands the xylem consists of scalariform 
tracheids, chiefly, while in the larger bundles there are parenchyma 
cells associated with the tracheids, and in a few instances tracheal 
tubes. The fundamental parenchyma sometimes contains stereome 
either as clusters of stone-cells, or masses of sclerenchyma fibers, 
as in the rhizome of Pteris aquilina, Fig. 465. The cortex also 
usually consists mainly of parenchyma, passing toward the exterior 





Fig. 466. 



Fig. 467. 



Fig. 466. — Longitudinal view of the rhizome of Aspidium, with the cortical 
portions cut away to show the cylinder of anastomosing bundles ; a, one of the 
branches of a bundle passing off to a leaf. Magnified about five diameters. 
Somewhat diagrammatic. 

Fig. 467. — Transverse section of rhizome of Aspidium, showing arrangement 
of bundles ; a, one of the bundles of the primary circle ; b, one of the branches 
passing off to a leaf; c, c, places where leaves have been cut away; d, thick- 
walled hypodermal cells. The unshaded portion is mainly parenchyma. Magnified 
about five diameters. 



into a thick-walled hypodermis. The fern structure is illustrated 
in the rhizome of the medicinal Male Fern, Dryopteris Filixmas. 
Here the principal bundles, which are from eight to twelve in 
number, are circularly arranged about a central parenchymatous 



226 



PART II. — HISTOLOGY. 



area which contains no bundles. Each bundle of the circle sends 
thick anastomosing branches to those adjacent to it, so that as a 
whole they form a netted cylinder, the stele. From this numerous 
smaller bundles pass outward through the cortex to supply the 
leaves (Figs. 466 and 467). 

In the stems of a few Ferns there is more than one circle of 
bundles. In the stems of Lycopodiums and Selaginellas there may 
be a single bundle, and this may be either concentric or radial, or 




Fig. 468. — Transverse section of the stem of Selaginella inaequalifolia, 
showing three fibro-vascular bundles separated from the fundamental tissue by 
intercellular spaces. (Sachs.) 

there may be two or more concentric bundles placed side by side, 
as in Fig. 468. In the stems of Equisetums, a transverse section 
of the internode shows a single circle of poorly developed collateral 
bundles surrounding a central hollow and having an endodermis 
on both inner and outer sides. Within each bundle at the inner 
side is an intercellular space, produced by the breaking down of 
the earlier formed xylem elements. A longitudinal section shows 
that the bundles run parallel in the internodes, but anastomose at 
the nodes where the bundles are received from the leaves. 

Monocotyledon Type. Here the stele contains a large number 
of bundles, usually of the collateral kind, and possessing no meri- 
stem tissue. »They are, therefore, closed bundles. As viewed in a 
cross-section of the stem, they are scattered with little or no 
apparent order through the fundamental tissue. The phloem part 



CHAPTER IV. — THE HISTOLOGY OF THE ORGANS. 



227 



of each bundle usually faces radially outward toward the periphery 
of the stem, and the xylem inward or toward the centre. The 
bundles of the stem are all continuous with those of the leaves 
and since the latter are usually broad and sheathing, the bundle? 
are very numerous. From the leaves, the bundles pass obliquely 
downward, or sometimes nearly horizontally inward, in a radial 
direction, toward the center of the stem; thence they bend in a 
downward direction, and then, in a long curve, sweep gradually 
outward toward the circumference of the central cylinder, where 
they finally terminate, after coalescing with other bundles which 
originate from leaves higher up. The bundles do not all penetrate 




Fig. 469. — Transverse section of the rhizome of Lily-of the- Valley (photo- 
micrograph), a, epidermis; b, cortex of parenchyma; c, end jdermis ; d, fibro- 
vascular bundle with V-shaped xylem ; e, fibro-vascular bundle with xylem 
surrounding the phloem (hadrocentric bundle). 



the cylinder to the same depth, some bend downward soon after 
entering it, others pass nearly or quite to its center. Hence the 
irregular arrangement observed in cross-section. It is evident also 



228 



PART II. — HISTOLOGY. 



that the bundles will be more numerous and crowded toward the 
periphery of the cylinder. The fact that stems of this type are 
denser exteriorly than they are in the center, is thus, in part at 
least, accounted for. In some plants the central portion of the 




Fig. 470. — Transverse section of Corn stem (photo-micrograph). a, the 
epidermiis ; b, one of the many scattered fibro-vascular bunlles (clcsed col- 
lateral type) ; c, the fundamental parenchyma. 



stele is destitute of bundles, and the thin- walled parenchyma of 
this region may even disappear at an early stage in the develop- 
ment of the stem, leaving a hollow, as in the stems of most 
Grasses. The bundles attain their best development in the mid- 
dle portion of their course. In their progress downward and 
outward they become thinner and less vascular; hence, in viewing 
a cross-section of a stem of this kind, the best developed bundles 
are found to be those farthest interior, while the more imperfect 
ones are the ones crowded together toward the outside of the cylin- 
der. The main points of structure in stems of this type are illus- 
trated in Figs. 469 to 473, inclusive. 



CHAPTER IV. — THE HISTOLOGY OF THE ORGANS. 



229 



Since the bundles do not possess a meristem layer, no increase 
in the thickness of the stem can take place except by the direct 
growth of the cells formed at the primary meristem. Accordingly, 
the majority of stems of this type do not increase in thickness 




Fig. 471. — Transverse section of a closed fibro-vascular bundle of the stem 
of Zea Mays. It consists of yxlem (g, g, s, r. 1) and phloem (v, v). The sur- 
rounding thick-walled tissue is the bundle sheath, p, p, thin-walled parenchyma; 
g, g. two large pitted vessels ; s, spiral vessel ; r. isolated ring of an annular 
vessel; 1, air cavity produced by rupture during growth. (Sachs.) 

except when quite young. This is true even when they live on 
from year to year; the stem of a Palm, for example, having the 
same diameter when two feet high that it has after reaching the 
height of one hundred feet. The growing area of the stem is 
confined to the apex or its immediate vicinity, and does not extend 
downward as a meristem cylinder between wood and bark, as it 



230 



PART II. — HISTOLOGY. 



does in the stems of Gymnosperms and Dicotyledons. In fact, in 
Monocotyls no true bark is found, nor is there a true pith, nor 
medullary rays, nor rings of growth. . 

There are some exceptional Monocotyledons, however, like the 
Yuccas and Dracaenas, whose stems do increase in diameter from 




Fig. 472. 



Fig. 473. 



Fig. 472. — Diagram showing course of bundles longitudinally in Monoco- 
tyledon type of stem. 

Fig. 473. — Part of transverse section of stem of a Dracyena. showing its mode 
of increasing in thickness, e, epidermis; c, corky layer; p, cortical parenchyma; 
f, a procambium bundle passing outward to a leaf; m, meristem layer, in which 
vascular bundles are forming ; g, newly formed bundle, the upper or outer part 
of which still consists of thin-walled cells ; s. secondary fundamental tissue, with 
radially arranged cells; t, primary fundamental tissue. (After Sachs.) 



year to year by means of a meristem zone in the thick primary 
cortex. In this layer secondary bundles are formed resembling 
those first formed in the stele of these and other. Monocotyledons. 
This mode of growth will be understood by reference to Fig. 47S. 



CHAPTER IV. — THE HISTOLOGY OF THE ORGANS. 231 

It should also be observed that there are a few anomalous 
Monocotyledons that have their bundles arranged in a manner 
quite different from that which has been described. In the common 
Yam and a few other plants the above-ground stems have the 
bundles arranged in a circle about a central pith, as in most 
Dicotyledons and Gymnosperms; and in some instances, as in 
Ruppia and its allies and in some Potamogetons, there is a single 
axile bundle which sends out branches to the leaves. 

Dicotyledonous Stems possess bundles of the open collateral 
type — i.e., comprising phloem (leptome), cambium and xylem 
(hadrome). These vascular bundles are arranged in a circle and 
separated from each other by the fundamental tissue composing 
the medullary rays and the pith. 

The secondary structure of dicotyledonous stems, resulting in 
growth in thickness, is due to the development of the cambium, 
which, as in the corresponding structure of dicotyledonous roots, 
forms new xylem on one face and new phloem on the other. 

At this point it becomes necessary to distinguish between the 
terms applied to the vascular bundles and their parts. Let it be 
understood, then, that mestome strand is not identical in meaning 
with fibro-vascular bundle although the terms are often employed 
synonomously. A mestome strand includes only the conducting 
elements of a fibro-vascular bundle, namely, the sieve-tubes, com- 
panion cells, and cambiform cells, constituting the leptome, and 
the tracheal tubes, tracheids and wood parenchyma, comprising the 
hadrome. Bast fibers (stereome) being mechanical elements are 
expressly excluded from the mestome, as are also, for the same 
reason, the libriform cells of the xylem. 

In dicotyledonous stems the course of the bundles from the 
leaves is inward and usually obliquely downward, and, having 
entered the stele, their course lies directly downward, keeping at 
about the same distance from the center of the stem. A cross- 
section of the stem, therefore, shows a circular arrangement of the 
bundles, which are of the collateral variety. They are usually 
shaped like a wedge, and radiate from a central portion of the 
fundamental tissue called the medulla or pith, toward which each 
presents its thinner edge. Separating the bundles laterally, and 
connecting the pith with the primary cortex are plates of funda- 
mental tissue called medullary rays. The inner or thinner portion 
of each wedge-shaped bundle is composed of xylem, and the outer 
or broader portion of phloem tissues, and these are ordinarily 



232 PART II. HISTOLOGY. 

separated from each other by a tangential layer of meristem tissue 
called the fascicular cambium. This is usually continued from one 
bundle to the next across the intervening medullary ray, and is 
here called the interfascicular cambium. The cambium thus forms, 
in most cases, a narrow zone, separating the phloem and exterior 
tissues, which constitute the bark, from the xylem and interior 
tissues, which constitute the woody region of the stem. These 
facts will be understood by reference to Figs. 474, 475 and 476 and 
their accompanying descriptions. 

In woody stems of this kind, every year during the season of 
growth, and for a time even in herbaceous stems, the cells of the 
cambium-layer divide in a tangential direction, and those interior 
and next to the wood are developed into xylem, and so add to the 
thickness of the woody region, while those exterior are developed 
into phloem elements, and increase the thickness of the bark. 

The activity of the cambium results most largely in the forma- 
tion of new wood (secondary ccylem) , both as a part of the primary 
bundles (proto-xylem) and by the interposing of secondary bun- 
dles between these. Along with the secondary bundles, new (sec- 
ondary) medullary rays are formed. This accounts for the various 
lengths of medullary rays sometimes seen in transverse sections of 
woody stems. Usually the medullary rays extend but a short 
distance vertically (1 mm. or less), though in some instances they 
run from node to node. 

The interior and older xylem tissues of woody stems commonly 
become strongly lignified and conspicuously different in color from 
the rest, owing to infiltrated coloring matter. This portion of the 



Fig. 474. — Portion of the young stem of Elder in tiansverse, radial- 
longitudinal and tangential-longitudinal views, showing primary structure of the 
dicotyl stem. (1) epidermis; (2) sub-epidermis (the mother cells of the 
phellogen) ; (3) collenchyma ; (4) parenchyma of the middle bark; (5) crystal 
cells, containing crypto-crystals; (6) resin tube; (7) bast fibers; (8) phloem; 
(9) cambium just developing; (10) tracheal tubes, of the primary wood; (11) 
parenchyma of the pith. T, added to a number indicates that the tangential 
view is presented, and R added to the number indicates the radial view of 
the tissue. 

Fig. 475. — Portion of the stem of Elder in transverse, radial-longitudinal 
and tangential-longitudinal views, showing secondary structure of the dicotyl 
stem. (1) epidermis, (2) mature cork cells, (3) immature cork cells, (4) phel- 
logen or cork cambium, (5) collenchyma, (6) parenchyma of the middle bark, 
(7) crystal-cells containing crypto-crystals, (8) bast fibers of primary struc- 
ture, (9) sieve-tissue of the phloem, (10) medullary ray, (11) cambium, (12) 
wood fibers, (13) tracheal tubes, (14) primary xylem, (15) parenchyma of the 
pith. T, added to a number, indicates that the tangential view is presented, and 
iR , added to the number indicates the radial view of the tissue. A, indicates 
the outer bark, B, the middle bark, C, the phloem or inner bark, D, the sec- 
ondary xylem, and E, the pith, except that the primarv xylem appears in this 
region also. 



CHAPTER IV. — THE HISTOLOGY OF THE ORGANS. 233 




Fig. 474. 
For description see page 232. 



234 



PART II. — HISTOLOGY. 




Figr. 475. 
For description see page 232. 



CHAPTER IV. — THE HISTOLOGY OF THE ORGANS. 



235 



wood, which has ceased to take any important part in the vital 
processes of the plant, is called duramen, or heart-wood, while the 
exterior zone of thinner-walled, uncolored and active cells is called 
alburnum, or sap-wood. 



I 





Fig. 476. — Transverse section of the rhizome of Menispermum canadense 
(photomicrograph), a. epidermis; b, parenchyma of the middle bark; c, crescent- 
shaped mass of bast ; d. phloem and cambium ; e. xylem ray ; f, medullary ray. 



In both stems and roots of Dicotyledons there may be distin- 
guished in the secondary xylem, produced each year, two well- 
marked parts, an early growth containing relatively more and 
larger tracheal tubes and a later growth in which the tracheal 
tubes are fewer and smaller and the wood fibers predominate. 
This difference in structure results from the need of water-con- 
ducting tissue at the time when the leaves are growing, while after 
this need has been supplied, chiefly strengthening tissue is formed. 



236 



PART II. — HISTOLOGY. 



Only the newer wood is connected with the vascular bundles of 
leaves and capable of supplying them with water. Thus are 
formed the rings of growth which are observed in the wood of 
trees that inhabit climates where there is a decided change of 
seasons, so as to produce periodical cessation of growth, and these 
rings are directly due to the juxtaposition of the small cells formed 
in the latter part of the season of growth and the larger ones 
formed at the beginning of the succeeding season. This will be 
understood by reference to Fig. 479. In climates where there is 
during the year one period of growth and one of rest, there will 
usually be formed one ring each year, and the number of rings in 





Fig. 477. — Transverse section of a young stem of Pine (photo-micrograph), 
a, cork ; b, one of many oil-vessels, embedded in the parenchyma of the middle 
bark ; c, the inner bark, including the phloem and medullary rays; (1), (2), 
(3). the first, second and third year's growth of wood (the specimen was 
gathered in early summer), showing small scattered oil tubes, the medullary 
rays, the xylem rays and two annual rings ; d, the pith. 



the wood, therefore, becomes an index, approximately, at least, of 
the age * of the stems. Sometimes, however, rings are due to 
other causes. Periods of drought in midsummer, accidental losses 



CHAPTER IV. — THE HISTOLOGY OF THE ORGANS. 



237 



of large branches possessing a great amount of leaf-surface, or 
other causes seriously interfering with regular growth, may result 
in the formation of two or more rings during a season. They must 





Fig 479. 



Fig. 478, A. and B. — Diagrams of the 
bundle system of the stems of Clematis 
vitalba, a Dicotyledon. 

A. Longitudinal view of upper part 
of stem, rendered transparent to show 
course of bundles, a, central cylinder or 
stele, showing six bundles arranged in a 
circle at its periphery ; b. b', bundles 
passing off to leaves ; c. c', rudimentary 
leaves near apex of stem. 

B. Transverse section of young inter- 
node, a, a bundle with an outer, phloem 
part, an inner, xylem part, and an inter- 
vening meristem area; b, pith; c, medul- 
lary ray ; d, primary cortex. Both re- 
duced from figures by DeBary. 

Fig. 479. — Small portion of transverse 
section of wood of White Pine, showing 
part of a ring of growth, a. The small 
cells at a. were produced near the close 
of the season's growth, and the large 
cells immediately to the left were pro- 
duced in the spring of the succeeding 
season. 



Fig. 478. 
not be relied on, therefore, as indicating with absolute accuracy 
the age of trees. 

The bark of Dicotyledons and Gymnosperms, when all the 
parts are present, consists of three layers, known as the outer 
bark, including the epidermis and the cork, the middle bark, chiefly 
parenchyma, and the inner bark or liber. 

The epidermis has already been described. In perennial stems 



238 PART II. — HISTOLOGY. 

it seldom persists for more than two or three years. When it first 
reaches maturity it forms, except where the stomata occur, a con- 
tinuous covering", though minute elevations may be discernible 
here and there on the surface, even before the close of the first 
year's growth. These are due to the growth of cells at certain 
points beneath. During the second year, the continuity is ruptured 
by fissuring at these points, and the cells from beneath protrude, 
giving to the surface a freckled or spotted appearance. These 
spots are technically called lenticels. They consist at first of loose 
parenchyma which soon breaks down, leaving a pore or opening- 
surrounded by a layer of cork. Through this pore, air is supplied. 
Lenticels thus replace the stomata as these are destroyed or ren- 
dered useless by the development of the bark. See Fig. 480. 

Sooner or later, however, a corky layer or periderm is formed 
by the division of cells in a tangential direction. This periderm 
may be formed superficially either by the division of the cells of 
the epidermis itself, as in the Willow, Apple and Oleander, or, as 
is more commonly the case, by the division either of the paren- 
chyma cells in immediate contact with the epidermis, or of those 
forming the second or third layer beneath it. In this case, the 
epidermis and the one or two layers of parenchyma that are thus 
cut off from supplies of nutriment by the formation of cork interior 
to them, die and disappear, and the cork and the secondary /men- 
stem (phellogen), in which new cork cells are formed, now con- 
stitutes the periderm. It increases in thickness by the formation 
of new cells in the phellogen by tangential division, but at inter- 
vals rows of cells divide in a radial direction, thus enabling the 
layer to keep pace, for a time, at least, with the growth of the 
stem in circumference. Examples of plants that form a periderm 
of this character are the Beech, Chestnut, Hazel and Bass-wood. 

The middle bark beneath this layer consists largely of paren- 
chyma cells, the outer layers of which are rich in chlorophyll. It 
is hence often called the green layer of the bark, for it is this 
which in young shoots, before the formation of a periderm, com- 
municates the green color to the surface, the cells of the epidermis 
being transparent. Some stems remain green for years because 
of the delay to form a periderm, and the persistence of the epider- 
mis. The Canada Moonseed (Menispermum canadense) affords an 
example. 

Not infrequently there occurs at the junction of this layer 
with the bast a ring or zone, it may be more or less interrupted, 



CHAPTER IV. — THE HISTOLOGY OF THE ORGANS. 239 

consisting partly of bast fibers and partly of stone cells, the so- 
called "mixed ring." Sometimes where this zone crosses the medul- 
lary rays it dips inward toward the centre of the stem, thus 
presenting a scalloped appearance when viewed in cross-section. 
Clusters of stone cells may also develop elsewhere.in this layer, and 
it may contain latex vessels, crystal sacs, secretion passages, etc. 
In stems where the layer persists, new cells are also formed either 
along the continuations of the medullary rays or elsewhere, so 
that it keeps pace with the general expansion of the tissues of 
the stem. 

It is by no means always the case that the periderm originates 
at or near the exterior. In many woody stems it originates inter- 
nally, in the deeper layers of the middle bark, or even in the 
innermost layer of cells where it joins the zone of bast fibers just 
described, or if that is not present, where it joins the other tissues 
of the inner bark. Thus, when the periderm is formed, not only 
may the epidermis disappear but also the greater part or even the 
whole of the middle bark, leaving only the inner bark covered with 
a periderm. The Juniper, Currant, Honeysuckle, Deutzia, Phila- 
delphus and Barberry are examples of plants that form a periderm 
in this manner. 

In the majority of woody stems when they become old, whether 
the periderm is at first produced superficially or from more deeply 
lying tissues, secondary formations of periderm occur in succession 
interior to those first formed, and the layers of dead tissues exte- 
rior to them, stretched by the growth of the stem, become rup- 
tured or fissured in various ways and peel off from the surface. 
These secondary layers of periderm may be formed in the middle 
bark or in the older portions of the bast ; hence, in the large trunks 
of many of our forest trees all tissues exterior to the liber have 
disappeared, * and, in the strict sense of the term, nothing of the 
bark but the inner layer is left. 

The liber is always present and always constitutes the most 
important portion of the bark. Although, as we have seen, its 
outer layers may peel off while being renewed from within, it 
always consists, when first formed, of the phloem of the fibro- 
vascular bundles, together with that portion of the medullary rays 
which separate these parts of the bundles laterally. It consists, 
therefore, largely of sieve and parenchyma tissues, with bast often 
intermingled. It not infrequently also contains other tissues, such 
as latex tissues, secretion cells, etc. The soft tissues of this layer 



240 



PART II. — HISTOLOGY. 



are particularly rich in albuminoid and other nutritious matters, 
and in medicinal barks it constitutes the area in which the active 
principles are usually found in greatest abundance. 

Since in perennial stems this layer increases in thickness year 
by year by growth in the cambium, it often, though not always, 
presents the phenomenon of rings of growth similar to those seen 
in the woody part of the stem. 

It is not arways the case that the stems of Dicotyledons con- 
form fully to the type which has been described. Cucurbitaceous 
plants, like the Pumpkin and Melon, have so-called bi-collateral 
bundles, that is, collateral bundles with an internal phloem; more- 
over, these bundles are arranged in two circles instead of one. 
Other curious deviations from the typical form occur in the stems 
of many tropical climbers known as "lianas." 

The stems of Gymnosperms show, for the most part, the same 
arrangement of the bundles as those of Dicotyledons. They differ 
from the latter mainly in the fact that the tissues, particularly 
those of the xylem, are less complex. In most cases the tracheal 
tubes and w T ood fibers which are so abundant in the xylem of Dico- 
tyledons are few in number or altogether wanting, these tissues 
being replaced, as we have seen, by disc-bearing tracheids. (Fig. 
477). 







Fig. 480. — Transverse section through lenticel of the White Birch, s, stoma; 
1, cells of the lenticel which, by their rapid increase in the inner layer, have 
caused an elevation of the epidermis, but have not yet burst through it ; e, 
epidermis. After DeBary. , 



The Leaf. — Leaves are specially modified expansions of the 
stem and in their incipient formation from the latter they develop 
from a primordial meristem (Fig. 481) with three primary meri- 
stems just as stems do (Fig. 482). From this growth arise the 



CHAPTER IV. — THE HISTOLOGY OF THE ORGANS. 241 

corresponding layers: epidermis, mesophyll and vascular bundles 
of the leaf. 

The epidermis of the leaf has substantially the same structure 
as that of the stem, except that it is usually more abundantly 




Fig. 481. — Mcristematic leaf structure of Corn in the plumule of the 
embryo; longitudinal section (photo-micrograph). 

supplied with stomata, particularly on its under surface. Here 
they are often very numerous. The leaf of Osmunda regalis has 
21,000 to the square inch, that of the Apple upwards of 150,000, 
and that of the Olive tree more than 400,000. The ordinary epi- 
dermal cells are also more apt to have lobed or irregular forms 
than those of the stem, as illustrated in Fig. 405. 

The vascular bundles of the leaf are usually composed of much 
the same elements as those of the stem with which they are con- 
tinuous, except that in their finer ramifications they become much 
depauperated, being often reduced to scarcely more than a row of 
tracheids surrounded bv elongated parenchyma cells constituting 
the bundle sheath. They follow the course of the veins and are 
a constituent part of them, though the veins include other tissue*- 
than those which properly belong to the vascular system (mes- 
tome). The bundles are usually collateral and destitute of a func- 



242 



PART II. — HISTOLOGY. 



tional cambium; the phloem portion faces the lower or outer 
surface, while the xylem faces the upper or inner surface. In the 
petiole there is either one large bundle or, more commonly, a mass 
composed of several pursuing a parallel course, at the stem end, 
becoming a part of its vascular system, and in the blade spreading 
out in various ways, according to the plans of venation already 
described. 

In the forked type, seldom seen except in Ferns and their allies, 
the bundles may spread out from the base of the leaf and run 
toward the margin, in which they terminate without anastomoses, 
or they may diverge from a median group of bundles or mid-rib, as 
shown in Fig. 483. 



A 




V"*>~'' 



Fig. 482. — Meristematic leaf structure of the 
Corn in more advanced stage ; transverse section 
of the terminal bud (photo-micrograph). 




Fig. 483.— Leaf- 
let of Osmunda re- 
galis, showing ar- 
rangement of vas- 
cular system. 



The parallel type is, as we have already seen, the prevalent 
one in Monocotyledons and Gymnosperms, though in exceptional 
instances it occurs among Dicotyledons, as in Eryngium yuccae- 
folium. 

It presents interesting variations. In the Pines a single median 
bundle is present, or two bundles enclosed in a common sheath but 
unconnected by cross-veins, run parallel to each other from base 
to apex of the leaf. In Welwitschia and most Monocotyledons the 
bundles run nearly parallel to each other from base to apex or 
margin, or from a median group of bundles, forming a mid-rib, to 



CHAPTER IV. — THE HISTOLOGY OF THE ORGANS. 24, °> 

the margin. Adjacent bundles are connected laterally by minute 
branches. The ends of the veins seldom terminate free, but curve 
toward each other and become united near the margin. See Fig. 
484. A few exceptional Monocotyledons belonging mainly to the 
Yam, Arum and Smilax families, have the bundles reticulately 
arranged, as in most Dicotyledons. 




Fig. 484. — Apical portion of leaf of Smilacina stellata, showing the arrange- 
ment of vascular bundles. 

In the reticulate type the bundles that enter the blade branch 
freely through it, running in all directions and anastomosing to 
form a net-work. The net-work may be fine or relatively coarse, 
but the meshes are seldom very regular, except in some Ferns 
which exhibit this type of venation. In many cases there are 
bundles which end free in the interior of the meshes, as in Fig. 
485; in others these are wanting, but some of the veins terminate 
free in the margin; in still other cases both modes occur in the 
same leaf. Compare Figs. 485 and 486. The main veins from 
which branches diverge to form the reticulum may be pinnately, 
radiately or costately arranged. In netted leaves the veins are 
usually more prominent on the dorsal surface of the leaf. 

As regards the arrangement of the mesophyll of the leaf three 
different types are distinguished: the dor si-ventral, the isolateral 
and the centric. / 



244 PART II. — HISTOLOGY. 

The dorsi-ventral is much the more common. In this there are 
usually two or more layers of parenchyma, rich in chlorophyll 




Fig. 485. — Part of vascular system of leaf of Cobaea scandens. 

(chlorenchyma) compactly arranged next the upper epidermis, or 
next the hypodermis, if the latter is present. These cells are elon- 




Fig. 486. — Part of vascular system of Bass-wood leaf. 



CHAPTER IV. — THE HISTOLOGY OF THE ORGANS. 



245 



gated in a direction perpendicular to the surface of the leaf, and 
hence the name palisade parenchyma has been applied to them. 
The other parenchyma cells of the leaf are usually very loosely 
arranged, being separated from each other by large intercellular 
spaces. They are hence called spongy parenchyma. The spongy 
parenchyma is the chief transpiring tissue and is protected by its 
position from too bright light and from too great evaporation. In 
leaves of this class, the color of the upper surface, owing to the 
compact arrangement of the chlorenchyma cells next to it, is 
usually a much deeper green than that of the lower surface. (See 
Figs. 487 and 488.) 




Fig. 487. — Transverse section of Belladonna leaf. eps. upper epidermis, and 

epi, lower epidermis with glandular trichomes ; pp. palisade parenchyma; pi, 

spongy parenchyma ; o, crystal cell ; v, xylem of the midrih ; r, medullary ray ; 
Is. and li, phloem. (Godfrin and Noel.) 



Isolateral Leaves differ from the preceding in having the 
palisade cells symmetrically distributed upon both sides of the 
spongy parenchyma, the latter occupying the interior of the leaf. 
Similarly, too, stomata are equally numerous upon both surfaces. 
(See Fig. 488a.) 

Centric leaves have but one kind of mesophyll cells and the 
veins are at the center, as in the Pines. Such leaves are cylin- 
drical or of a similar shape and do not present a distinct upper 
and under surface. (Fig. 489.) 

In all leases, the stomata are placed directly over intercellular 



246 



PART II. — HISTOLOGY. 



spaces, so that there is free communication between the interior 
of the leaf and the outside. Collenchyma is frequently met with; 




Fig. 488. — Transverse section of a leaflet of Cycas revoluta (photo-micro- 
graph), ue, upper epidermis with one row of sub-epidermal cells; le, lower 
epidermis with sunken stomata ; pp, palisade parenchyma ; sp. spongy paren- 
chyma ; cc, conducting cells. 




Fig. 488a. — Portion of a transverse section of Eucalyptus leaf, epi, epi- 
dermis of inner surface ; epe, epidermis of outer surface ; pp, palisade parenchyma 
extending from epidermis to epidermis; f, oil gland; In, lenticel ; sc, bundle of 
sclerenchyma at the leaf margin ; hi, and he, hypodermis beneath the epidermis 
at the principal veins ; fi and fe, bast fibers on the inner and outer faces of the 
fibrovascular bundles; li and le, phloem on the inner and outer faces of the 
xylem which consists of vessels, v, separated by medullary rays, r. (Godfrin and 
Noel.) 



CHAPTER IV. — THE HISTOLOGY OF THE ORGANS. 



247 



strands of stereome often accompany the bundles, usually adjoin- 
ing and outside of the phloem. Peculiar, branched sclerotic cells 
sometimes occur in the mesophyll, notably in Tea. 

The Flower. — Morphologically, flowers may be considered modi- 
fied branches, the parts of the flower being analogous to leaves 
arranged upon a shortened stem (the receptacle). Floral leaves 




Fig. 489. — Transverse section of Pine leaf (photomicrograph). a. the 
epidermis with sunken stomata ; b, sub-epidermis ; c, chlorenchyma, with infolding 
walls; d, oil-tube; e, endodermis ; f, one of the two hbro-vascular bundles, 
showing phloem above and xylem below. 



therefore resemble foliage leaves and, like the latter, their histo- 
logical elements consist of a framework of bundles, parenchyma 
filling the spaces between these, and a surrounding epidermis. 

The receptacle and peduncle likewise resemble the leaf -bearing 
stem. 

The sepals are usually green, and bear the closest resemblance 
to assimilative leaves. When green, they bear stomata on the 
outer face. Trichomes are frequently present. 

The petals are destitute of chloroplasts and are usually colored 
either by chromoplasts or by substances dissolved in the cell-sap. 
The velvety appearance possessed by many petals is due to papillae, 
very short cell projections. The mestome or conducting strands 
of petals are greatly attenuated and their mesophyll is reduced to 
a thin layer of branching, spongy parenchyma cells. In fact, as 
compared with foliage leaves, the whole structure of the petal is 
much more delicate (see Figs. 406 and 490). 



248 



PART II. — HISTOLOGY. 



The Stamens consist of parenchyma covered by an epidermis 
and bearing a slender bundle or mestome strand passing through 
the filament and connective. The pollen sacs possess a fibrous 
hypodermal layer, the endothecium, which determines their dehis- 
cence. The tapetum which lines the pollen sacs during their 




/ 



f 




Fig. 490. — Petal of House Geranium, showing the delicate, anastomosing 
venation. 

development nourishes the pollen grains and disappears at their 
maturity. The pollen grains are either single cells or groups of 
few cells, containing cytoplasm and surrounded by an outer and 
an inner wall, the outer wall being thickened externally by various 
and peculiar markings. Besides cytoplasm and nuclei, pollen 
grains contain stored food, commonly oil or starch. (See Fig. 491.) 
The cells of the Stigma secrete a viscid, saccharine substance, 
and are frequently prolonged upward, forming papillae. 



CHAPTER IV. — THE HISTOLOGY OF THE ORGANS. 249 

The Style consists in its interior portion of a loose conducting 
tissue, or may even be tubular, thus favoring the passage of the 
pollen tube. 

The Ovary consists of tissues which are as yet in an undevel- 
oper condition, but which later form characteristic parts of the 
fruit. Upon the inner surface of the ovary is borne the Placenta, 
through which pass mestome strands whose branches lead to the 
ovules. The structure of the ovule has already been described 
(page 93). It is joined to the placenta by a stalk which contains 
a strand of conducting tissue. 

The Fruit and the Seed. Since the fruit includes not only the 
ripened pistil or pistils but also such adhering portions of the 
perianth or of the receptacle as may develop along with the pistil 
and remain attached to it, it is evident that fruits may vary widely 
in character, botanically, yet they present no new tissues histo- 
logically. The fruit may possess: (1) An epidermis of the usual 
kind and bearing some or all of the usual appendages, stomata 
being, however, much less common than in leaves. (2) A hypo- 
dermis, underlying the epidermis and sometimes quite distinctive. 
(3) Sclerotic tissue, varying greatly in character and amount in 
different fruits, being very abundant in hard, dry fruits and often 
absent in others. (4) Parenchyma tissue, especially abundant in 
fleshy fruits and which may contain the various cell contents. 
Secretion receptacles, oil tubes, latex vessels, oil cells, etc., may be 
associated with the parenchyma or extend through it. (5) Vas- 
cular bundles (mestome), usually slender and destitute of fibers, 
extending through the parenchyma. 

The portion of the fruit enclosing the seed is called the peri- 
carp, and three parts of it are distinguished: (1) The epicarp, 
the outer part, consisting practically of the epidermis only. (2) 
The mesocarp or sarcocarp, which, when present is the middle 
layer, and is the fleshy part of many fruits. (3) The endocarp 
or inner part, which may include the inner epidermis and sclerotic 
tissue. 

The seed is composed of: (1) The seed coat (spermoderm), 
which includes the testa, or outer coat, and the endopleura, or 
inner coat. These coats are made up of an epidermis, seldom 
bearing stomata, but frequently trichomes, the latter being often 
characteristic, as in Nux Vomica and Gossypium. Quite fre- 
quently, too, the epidermis is mucilaginous in nature, as in Linum, 



250 



PART II. — HISTOLOGY. 



and Sinapis. Sometimes the epidermis may be more or less ligni- 
fied, as in Amygdala. In addition to these features, peculiar 
markings are often formed through the arching of the thickened 
outer wall (cuticle) of the epidermal cells, as in Staphisagria. 




Fig. 491. — Pollen-grains: 1. Cobaea scandens. 2. Morina Persica. 3. Cucur- 
bita Pepo. 4. Passiflora Kermesina. 5. Circasa alpina. 6. Convolvulus sepium. 
7. Cannabis sativa. 8. Pinus Pumilio. 9. Mimulus moschafus. 10. Albucca 
minor (dry and moistened). 11. Dianthus Carthusianorum. 12. Condalis lutea. 
13. Gentiana rhc&tica. 14. Salvia glutinosa. (Kerner and Oliver.) 



The side walls of these cells are in some cases characteristically 
sinuous, as in Stramonium and the seeds of the Grasses. Under- 
lying the epidermis are sclerotic tissue, pigment cells and paren- 
chyma in varying amounts. (2) The kernel, located within the 
seed-coats, and consisting of the embryo only or of the embryo and 
the surrounding endosperm. The tissues composing the embryo 
are meristematic, but parenchyma constitutes the storage portion 
and its cells are filled with nutritive contents, such as starch, 
aleurone and fixed oil. The cells composing the endosperm are 
usually thin walled and stored with food, but may in some cases 



CHAPTER IV. — THE HISTOLOGY OF THE ORGANS. 251 

be thick-walled and horny, as in Nux Vomica and Coffee, where 
the walls consist of reserve cellulose. Similar to the endosperm 
but differing in origin is the perisperm or nucellar tissue, usually 
insignificant but in some cases, notably in Pepper and Cardamom, 
composing the bulk of the starchy part of the seed. 

Practical Exercises. 

1. For the study of Dicotyl stem structure, make sections transverse and 
longitudinal of a stem of Menispermum canadense, selecting one that has attained 
a season's growth. This is selected for the first study, because the bundles are 
sharply distinct from the other tissues, the medullary rays being broad, unligni- 
iied and composed of thin-walled cells, and various kinds of tissues are well 
developed. It also affords a simple and easily understood example of stem struc- 
ture. The sections should be cut thin, and care should be taken that the longi- 
tudinal ones run as nearly lengthwise of the grain as possible. To get a clear 
understanding of the structure, some of the longitudinal sections should be 
radial and others tangential. A radial section, it will be remembered, is one 
which passes through the middle of the stem lengthwise, — that is, along the 
medullary rays, — while a tangential section is made to one side of the center, 
so as to cross the direction of the medullary rays. The sections used for imme- 
diate study should be placed on a slide, treated with a drop of phloroglucin solu- 
tion, and then, after the solution has had time to thoroughly penetrate the 
tissues, but before the liquid has evaporated from the cells, put on a drop of 
chloral h} drate solution, cover the section with a cover-glass and examine. The 
tissues of the xylem, the bast cells of the phloem and other lignified tissues will, 
by this process, be stained a bright red, while the unlignified tissues, such as 
most of the pith cells, the medullary ray cells, the cortical parenchyma, the sieve 
tissues and the cambium cells will not be stained. 

Some of the longitudinal sections should be treated with Schulze's mace- 
ration fluid for the purpose of isolating the tissues and studying them in detail. 

After the structure and arrangement of the tissues of this stem are well 
understood, similar studies, for the sake of comparison, should be made of twigs 
of the Bass-wood, Apple, Maple, Witch Hazel, or other common woody plants, 
and the resemblances and differences of structure carefully noted ami described 
by the aid of drawings. 

The stems of several herbaceous Dicotyledons, such as those of the Begonia, 
Buckwheat, Datura, Cow Parsnip and Common Milkweed, should now be studied 
in the same way. 

Make similar studies, also, of the stems of aquatic Dicotyledons, such as the 
Water Chinquepin, the White Water-lily, the Yellow Water-lily, etc. 

In what respects do the bundles of the above-named stems of herbs and 
aquatics differ from those of the woody stems you have studied? 

2. For the study of Monocot) ledon stem structure, first make thin sec- 
tions of the stalk of the common field Corn, treating the sections in the same way 
as it was directed to treat those of Menispermum. Note the distribution of the 
bundles, and then study their structure, the relative arrangement of xylem and 
phloem, the tissues composing each, and determine whether or not they are 
separated from each other by a cambium area ; study what tissues of the stem 
are lignified, and what ones unlignified, and note the tissues of the hypodermis, 
observing whether -they are fibrous or not, the extent to which their walls are 
thickened, etc. 

Now compare with this, sections of the stems of other herbaceous Mono- 
cotyledons, such as the Spiderwort, Canada Lily, Tuberose, and Wheat. 

Compare, also, sections of the stem of a woody Monocotyledon, as that of 
vSmilax or Rattan, and note carefully the structural differences. 

Lastly, compare sections of aquatic Monocotyledons, such as Pickerel Weed, 
Bulrush, and Calamus. 

3. For the study of the Fern stem, make similar studies of the rhizome 
of Pteris aquilina, of Aspidium marginale, and of Polypodium vulgare. 

4. For the study of root structure, first make sections of the rootlets of 
the Sweet Flag or Calamus, or of the Virginia Spiderwort, preparing sections 
as beiore. Identify the xylem (hadrome) rays and the alternating phloem 
masses' Cleptome) ; determine the number of strands of each, and the kinds of 



252 PART II. — HISTOLOGY. 



cells which compose them. Identify the pericambium and the endodermis, and 
study the character of the cells which compose each. 

With these, compare sections of the roots of other Monocotyledons, such as 
those of Indian Corn, Amaryllis, Indian Turnip and Calla, making drawings and 
descriptions of the central stele in each case. 

Make similar sections and studies of the root of some herbaceous Dicotyledon, 
such as that of the common Buttercup, or of the American Cowslip, and of some 
Fern, such as Osmunda cinnamomea, and observe that in all essential respects 
the structure is the same as that of the roots previously studied. 

Now cause a few beans or peas to germinate, and make transverse sections 
of the primary root in different stages of its development. Note that, when 
young, its structure corresponds with the rest, but afterward it undergoes import- 
ant secondary changes. By means of a series of sections, study the successive 
stages of these changes, recording your observations by aid of drawings. 

5. For the study of the arrangement of the bundles in leaves, obtain the 
following:, the fork-veined leaflets of the Cinnamon Fern or of the Maiden-hair 
Fern; the parallel-veined leaves of the Lily-of-the- Valley or of Solomon's Seal; 
and the reticulate leaves of the Wild Cranberry, of the Maple and of the Wild 
Cucumber (Echinocystis). In order that the finer ramifications of the veins 
may be distinctly sc n, it is best that the leaves should first be bleached and then 
stained. Soak them for a few days in alcohol to remove the chlorophyll, then 
transfer them to Labarraque's solution, and let them remain until colorless, but 
not so long as to cause their disintegration. They must now be soaked for some 
time in clean water, or better, be allowed to remain for some hours in running 
water, until the last traces of the odor of chlorine have disappeared. They 
should then be allowed to stand for a little time in water slightly acidulated with 
hydrochloric or nitric acid, and then transferred to a very dilute aqueous solution 
of methyl-green and permitted to remain until the veins have become distinctly 
stained. They may then be rinsed in clean water and examined. The lignified 
tissues of the veins are more deeply stained by this process than the rest of the 
structure, and the mestome strands may, therefore, be readily traced. Such 
preparations may be mounted in balsam, and if the preparations are not much 
exposed to light, the aniline stain will persist for years. 

6. For tre study of the internal structure of bifacial leaves, take almost any 
flattened leaf, like that of the Currant, Beech, or American Elm, and place it 
between two pieces of Elder pith and make thin slices transversely, with a razor, 
transferring the sections to water as fast as made. By aid of a camel's hair 
brush, float some of the thinnest ones upon a slide, cover with a cover-glass and 
examine. Observe the vertically elongated palisade cells beneath the upper 
epidermis, the loosely arranged parenchyma farther interior, and the somewhat 
more compactly arranged parenchyma next the lower epidermis. In the lower 
epidermis, also, a sectional view of stomata may be obtained. Observe that these 
each communicate with a large intercellular space. Study the section of a vein, 
and observe what kind of bundle it represents, also the position of the phloem, 
as respects the lower epidermis. 

The leaf of the Sago Palm (Cycas revoluta) shows the typical dorsiventral 
structure, though it is much more woody than are ordinary leaves. This lignifica- 
tion, however, gives rigidity and enables one to prepare sections more readily. 
Using the method described above, cut sections crosswise and lengthwise of the 
leaf and parallel with the upper surface. In the transverse section, observe that 
the epidermis is covered by a thick cuti,cle, more noticeable on the upper surface, 
while the upper epidermis is reinforced as well by a lignified hypodermis. The 
underlying palisade parenchyma is rich in chlorophyll. If leaves that have been 
kept in alcohol are used, the green color will have disappeared but the plasties 
remain. The spongy parenchyma is not typical in this view. The stomata are 
peculiar in structure owing to the "vestibule" in front of each pair of guard 
cells, Fig. 488. In the longitudinal sections the intercellular spaces in the spongy 
parenchyma are evident, while the tangential (surface-parallel) section shows the 
intercellular spaces in the palisade tissue. Examine a surface section from the 
lower side of the leaf and notice the appearance of the stomata in this view. 

By a similar method, the structure of isolateral leaves may be studied. For 
this purpose, leaves of the Wax-plant (Hoya caruosa), or of the garden Portu- 
lacca, may be used. Here, it will be observed, no distinct palisade tissue is 
developed, and there is little difference of structure between the upper and under 
sides of the leaf 

Now compare with these the leaf of the common White Pine, making thin 
cross-sections of it and studying it with care. Observe the excessively thick- 
walled epidermal cells, the well-developed hypodermis, the large intercellular 
spaces beneath the stomata, the peculiar chlorophyl-bearing parenchyma cells 
with internally folded walls, the scattered resin-passages, and the pitted paren- 



CHAPTER IV. — THE HISTOLOGY OF THE ORGANS. 253 



cliyma cells and l'tbro-vascular bundles, both enclosed within the bundle sheath. 
Fig. 489. 

7. For the study of sepals and petals with reference to the venation, the 
presence or absence of stomata, the character and distribution of the coloring 
matter and the cause of the velvety appearance which some parts possess, the 
dowers of Tropeolum majus, of Torenia Asiatica, and of the common Pansy may 
be selected. Cross-sections may be made in the same manner as was directed for 
ordinary leaves. 

8. As a study of fruit, examine common Garden Pepper (Capsicum annuum). 
This fruit has a thick pericarp enclosing a large cavity divided below into three 
compartments by a central placenta which bears numerous seeds. In the upper 
part of the fruit these three compartments become confluent and the placenta 
changes to the parietal type. 

A section through the pericarp displays an epicarp consisting of epidermis 
having a very thick outer wall (cuticle), a mesocarp composed of several layers 
of collenchyma the walls of which are suberized, and parenchyma containing 
drops of oil and red chromoplasts, to which the .red color of the fruit is due. 
The unripe, fruit is green in color arid in it this layer contains chloroplasts and 
some small starch grains. The inner part of the mesocarp is marked by a row 
of very large, empty cells (giant cells). Then follows the endocarp made up of 
alternating groups of elongated cells with a wavy outline, one group consisting 
of lignified sclerotic cells having distinct pores while the adjoining group is 
thin-walled. 

A transverse section of the seed shows a spermoderm possessing a peculiar 
epidermis. The outer wall of these epidermal cells remains thin while the inner 
and side walls are excessively thickened and lignified. These thickenings of the 
inner wall project inward into the cell-cavity in oddly-curved masses, giving 
rise to intestine-shaped convolutions which are highly characteristic. 

The parenchyma of the endosperm is rich in aleurone and fat. The embryo 
is of similar tissue but more delicate. 

Compare surface sections of the outer and the inner epidermis from the 
pericarp and the epidermis of the seed, staining for lignin. 

9. Study the fruit of the Fennel. This is a cremocarp, and is composed 
of two plano-convex half-fruits termed mericarps. Each mericarp is marked 
by five obtuse ridges, and between these are from six to eight oil tubes. Each meri- 
carp contains a single seed. A transverse section of the mericarp displays the 
following structure : The epidermis is narrow, inconspicuous, destitute of tri- 
chomes and with few stomata. Enclosed within it is parenchyma tissue con-* 
taining the oil-glands, which are intercellular spaces lined by specially modified 
cells of a deep brown color. Extending through the parenchyma, and underlying 
each ridge, lies a vascular bundle, and two more lie near the flat (commissural) 
surface on the inner side of the mericarp. 

The endosperm is hard and is composed of thick-walled parenchyma cells 
filled with aleurone and fixed oil. The embryo is of similar tissue. 



PART III. 

PHYSIOLOGY. 



CHAPTER I. 



SCOPE OF PLANT PHYSIOLOGY. — PROPERTIES OF PROTOPLASM. 

Plant Physiology treats of the functions of plants, or in other 
words, of the way plants do their work, whether of vegetation or 
of reproduction. We have already touched upon this subject. In 
Parts I and II, where we described the mechanism of plants, we 
had, incidentally, more or less to say about the functions of parts 
and of various processes that go on in the plant. What was there 
said need not here be repeated, but it remains still to be explained 
how the plant, as a whole, performs its functions; how it absorbs, 
digests and circulates its food; how, through the organs it pos- 
sesses, it makes use of the chemical and physical forces of nature 
to maintain its life, to build up its tissues and to reproduce its 
species. 

All the activities which a plant exhibits are due to the wonder- 
ful substance, protoplasm, the appearance and structure of which 
have already been described. While the protoplasm lives the plant 
goes on building up its tissues, appropriating constituents of the 
soil and air to repair its wastes, and exhibiting all the profoundly 
interesting phenomena which belong to life; but when it dies, the 
intricate structure which it had built up, and of which it formed 
a part, falls rapidly into ruins, and the complex molecules con- 
structed by its agency speedily decompose into simpler forms. 

The properties or attributes of protoplasm, that is, those which 
serve to distinguish it from all other substances, have already been 
mentioned in part, but may be more fully stated as follows : 

1. Contractility or mobility, the power to change its form by 
virtue of forces which reside within. 



CHAPTER I. — PROPERTIES OF PROTOPLASM 255 

2. Irritability, or the power to respond to stimuli, such as heat, 
light, moisture and gravity. 

3. Conduction, the power of transporting substances in definite 
courses through itself; including the absorption and excretion of 
such substances. Since these substances are necessarily conveyed 
in aqueous solution, the property of conduction implies also per- 
meability to water, perhaps the most noteworthy single character 
of living protoplasm. 

4. Metabolism, the sum of the changes, chemical and physical, 
which take place in the protoplasm. Metabolism may be construc- 
tive or destructive. Constructive metabolism (anabolism) com- 
prises the building up of complex substances from simpler com- 
pounds. Photosynthesis, whereby the active energy derived from 
the sun is stored up as potential energy in the form of carbo- 
hydrate, is an anabolic process. Destructive metabolism (katabo- 
lism) comprises the breaking down of complex substances into 
simpler forms, with the accompanying release of energy. Respira- 
tion is a typical katabolic process. We know little of the actual 
mechanism of metabolism but we have reason to believe that the 
enzymes secreted by the protoplasm are intimately connected with 
it and perhaps govern it. 

The constructive and destructive processes are going on con- 
stantly and, of course, simultaneously. 

When, as is usually the case, the constructive process overtops 
the destructive and more material is added than is given off, we 
have groivth, to which, in turn, development and reproduction are 
closely allied. If, on the other hand, the waste exceeds the repair, 
we have decay, which if carried on too far, results in the death 
of the organism. 

These properties not only sharply distinguish living from non- 
living matter, but all living protoplasm, both animal and vegetable, 
possesses them in a greater or less degree. They are interdepen- 
dent, being closely bound up one with another. Thus the power 
of contractility lies at the foundation of all movements in animals 
and plants. Motion is a less conspicuous phenomenon in plants 
than in animals, but it is no less real. The higher plants show it 
in the. slow movements of all young and growing organs, in the 
movements of the living matter within the cells, in the bending of 
organs toward or from the light, or toward or from the earth, and, 
more conspicuously, in such movements as those of the upper inter- 
nodes of climbing plants, of tendrils, of the leaves of some Mimo- 



256 PART III. — PHYSIOLOGY. 

sas, of Venus' Fly-trap, etc., but they arc destitute of the power 
of locomotion, or of moving from place to place as the higher 
animals do. On the other hand, while some of the lower forms of 
animal life are fixed, some of the humblest of plants are conspicu- 
ously locomotive. Moreover, the modes of locomotion are, in many 
cases, identical with those observed among the simpler forms of 
animals. The Slime Molds, for example, move from place to 
place by a slow, creeping process, accompanied by constant changes 
of form, precisely as in the case of the Amoeba and kindred animal 
organisms, and Protococcus, in one stage of its life history, Pando- 
rina and Volvox move by means of cilia the same as the Infusoria ; 
so do likewise the zoospores of many cryptogams. 

As regards irritability, that which plants exhibit is, of course, 
less in degree than that which, in the higher animals, rises into 
sensibility and sensation, but it can hardly be doubted that it is 
the same in kind. 

In animals this property is mainly concentrated in a highly 
specialized tissue called nerve tissue; hence its phenomena are 
strikingly evident, while in plants it is diffused through all the 
living tissues, and is in most cases but feebly manifested. But 
these differences do not hold when we come to compare the lowest 
forms of animal life with plants. In the lowest animals there are 
no nerve cells ; the property of irritability is diffused, as in plants. 
The Dionaea, the Sundew and the Sensitive Plant exhibit a degree 
of irritability which equals, if it does not exceed, that shown by 
the lowest animal types. Moreover, every gradation is observed 
between the irritability of a tendril or a radicle and that shown 
by the higher animals. The conclusion therefore is irresistible, 
that the property is fundamentally the same in animals and plants 
— that irritability is an endowment of all living protoplasm. 

Respiration, also, which is essentially an oxidation process, 
involving the taking in oxygen and throwing off carbon dioxide, 
is much less evident in plants than it is in animals, though cer- 
tainly it is no less real. It is a less noticeable phenomenon in 
plants, partly because, being less active organisms, they waste less 
rapidly than animals do, and the respiratory process is conse- 
quently slower; partly, because it is not carried on by means of a 
special breathing apparatus, as it is in those animals with which 
we are best acquainted, but more, perhaps, because in ordinary 
green plants the process is masked in the daytime by the photosyn- 
thesis which goes on at the same time. In the latter process, 



CHAPTER I. — PROPERTIES OF PROTOPLASM. 257 

carbon dioxide is utilized for the production of food, in quantities 
larger than that given off in respiration; and the amount of oxy- 
gen which is consumed in respiration is more than counterbalanced 
by that set free in photosynthesis. For this reason, it is difficult, 
in the daytime, to demonstrate the respiratory process- in green 
plants. But at night, photosynthesis, being dependent on sunlight, 
is suspended, while respiration, which goes on continuously, can 
readily be discovered by appropriate experiment. 

The facts of respiration in plants have also been demonstrated 
by experiments on fungi and other plants destitute of chlorophyll, 
as well as on seeds, roots and other chlorophylless parts of green 
plants, and which, therefore, cannot make use of carbon dioxide. 
Here the consumption of oxygen and liberation of carbon dioxide 
is found to go on continuously, as in fact it does in all living cells. 

All living organisms are also in substantial agreement as 
regards destructive metabolism. In both animals and plants the 
energy which is required for carrying on the various phenomena 
of life is derived from the breaking down of complex into simpler 
matters by processes of oxidation. In both, complex compounds 
with much potential or passive energy become simpler compounds 
with little or no potential energy, and the difference becomes 
kinetic or active energy in the form of heat, electricity and motion, 
giving rise to the various activities of the organism. Here lies the 
significance of the respiratory process. In this transfer of matter 
from a higher to a lower potential, oxygen is consumed, and 
gaseous carbon dioxide escapes as one of the products of the. 
change, The organism is therefore in many respects comparable 
to an engine in which the latent energy of the fuel is converted 
into work, while during the process, the wood or coal passes into 
carbon dioxide and water which are no longer available as sources 
of energy. 

The products of metabolism are not always the same in the 
plant as in the animal, but the differences are only such as can 
readily be accounted for by differences of habit; indeed, they are 
scarcely greater than those existing between animals of widely 
different habits. 

The divergence between plants and animals is perhaps widest 
in the matter of photosynthesis or constructive metabolism. Green 
plants have a power not possessed by most animals, of raising 
inorganic matter into complex organic compounds. Thus they 
derive their sustenance directly from the inorganic world. From 



258 PART III. — PHYSIOLOGY. 

the interaction of water and carbon dioxide they form a carbo- 
hydrate, and then, by bringing this into other combinations, or 
causing it to pass through other chemical changes, they use it to 
build up their tissues. This the animal cannot do; he is dependent 
for his sustenance on already organized matter. He is, in fact, 
indebted for his very existence to the constructive work of the 
plant. But this distinction, which separates with apparent sharp- 
ness the chlorophyll plant from the ordinary animal, is not univer- 
sal. Most parasitic and saprophytic plants, being destitute of 
chlorophyll, are, like the animal, dependent on organic food mate- 
rials for their existence. Moreover, chlorophyll plants are not 
green throughout ; a part of the cells contain green coloring matter, 
but another part, often the larger part of the plant, contain none 
whatever. These cannot manufacture their own food-materials; 
they are dependent for their sustenance on the organic matters 
elaborated by the green cells. In the way they are nourished they 
agree essentially with animals, yet their origin is the same as that 
of the chlorophyll-cells with which they are associated; both are 
products of cell-division from the original germ-cell. 

Lastly, as regards the modes of reproduction. Here again the 
parallelism between animals and plants is very complete and strik- 
ing. Among both are found organisms which reproduce by cell 
division, in its various modifications of budding, fission and inter- 
nal cell-formation. Many animals bud and branch like plants, and 
some of these approach so nearly to plants in appearance and habit 
of growth that it requires careful observation to distinguish them. 
The lowest animals, like the lowest plants, reproduce by cell divi- 
sion only; organisms a little higher in the scale, in each kingdom, 
reproduce by conjugation or the union of two similar cells; and the 
highest animals, as well as the highest plants, reproduce by ferti- 
lization, or the union of two different cells. 

Plants and animals, therefore, resemble each other fundamen- 
tally; the protoplasm, which constitutes the physical basis of life 
of both, has in both the same essential properties. We must regard 
plants and animals as two branches of a common trunk. The first 
living being that made its appearance on our globe was probably 
neither distinctly plant nor animal, but a bit of undifferentiated 
protoplasm. From such a form, as a common trunk, have 
diverged the two great branches of the tree of life, each of which, 
by countless ages of growth, and repeated branching, has given 
rise to an innumerable and richly varied series of forms. 



CHAPTER II. — CONSTITUENTS OF PLANTS. 269 

CHAPTER II. 

CONSTITUENTS OF PLANTS. — FOOD OF PLANTS. — ABSORPTION OF WATER 

AND SOIL SOLUTIONS. — ASCENT OF WATER. — TRANSPIRATION. — 

GASES IN PLANTS. 

Constituents of Plants. By dessicating a plant at a temperature 
too low to cause chemical decomposition, we find it loses greatly in 
weight, owing to the evaporation of water, which always forms a 
large part of the substance of the living plant. The amount, how- 
ever, varies greatly in different plants, and in different portions of 
the same plant. In aquatics, it often reaches 95 per cent, while 
in the wood of some trees, it may fall as low as 20 per cent. The 
average for herbaceous plants is probably not far from 75 per 
cent. It pervades all parts of the organism. The vacuoles of every 
protoplast contain water in greater or less quantity. In dry seeds 
this amount may be very small, but in active and growing parts 
the protoplasm must have sufficient water to maintain it in a semi- 
fluid condition. Indeed, naked cells live only in water or in wet 
places, and when the protoplasts of any plant are thoroughly dry 
their life is usually extinct. The wilting of plants when deprived 
of water is familiar, and the crispness of leaves and other soft 
parts is due to the water that fills their cells. 

The food of the plant must be supplied in watery solution in 
order to be usable; the waste products are excreted through the 
same medium, and even the raw materials, both the gases from 
the air and the soil substances, are brought to the protoplasts in 
aqueous solution. Growth, also, is dependent on water supply. 

If the dried plant be burned, the larger portion of its substance 
will pass off in the form of gases, consisting of watery vapor, 
carbon dioxide, etc., while another portion, varying in amount 
according to the nature of the plant, will be left behind as ash. 

Quantitative determination of the ash shows a variation in 
amount in the different organs of the plant; the ash yield of leaves 
is greater in proportion to weight than that of woody stems or 
roots. Therefore ash determinations are of value in establishing 
the purity of many drugs. However, the character of the soil and 
other external conditions may influence the amount as well as the 
composition of the ash, which also varies with the species of the 
plant; thus samples of Digitalis leaves give an ash content ranging 
from seven to fourteen per cent, while Henbane leaves normally 



260 PART III. — PHYSIOLOGY. 

yield from twenty to thirty per cent of ash. Guaiac wood, noted 
for its hardness and weight, yields not more than three per cent, 
and Gum Arabic scarcely more, about four per cent. 

Qualitative analysis shows the ash of plants to consist chiefly 
of Potassium, Sodium, Calcium, Magnesium and Iron, among the 
metals, and Chlorine, Sulphur, Phosphorus and Silicon among the 
non-metals. 

In that portion of the dessicated plant which passed off as car- 
bon dioxide and watery vapor when the plant was burned, we would 
find the elements Carbon, Hydrogen, Oxygen and Nitrogen. Of 
these, carbon in the form of charcoal is most familiar. Ordinarily 
carbon constitutes about half of the weight of the dried plant. 

Carbon, oxygen, hydrogen, nitrogen, potassium, magnesium, 
phosphorus, sulphur and iron are essential to all plants. The first 
three are the constituents of all carbohydrates, as starch, cellulose, 
sugar, etc.; in addition to these, protoplasm contains, as essential 
constituents, nitrogen and sulphur. Potassium and phosphorus, 
though not properly constituents of protoplasm, are always found 
in relation to it, and closely associated with the activities of the 
plant. The former appears to be essential to the formation of 
starch, and to be concerned, also, in its transfer from one part of 
the plant to another, while the latter, though its functions are not 
well understood, enters as an essential constituent into some of 
the important organic compounds of the plant, as, for example, 
nuclein and chlorophyll. In the form of the phosphates, it also 
promotes the process of metabolism in the cells, and, probably by 
rendering albuminoid matters more soluble, aids the transfer of 
these important substances. Calcium is necessary for the higher 
plants, though fungi can develop without it, and sodium chloride 
is commonly required by seaweeds.. 

Among the non-essential constituents is silicon, which occurs 
in the form of silica, is widely distributed and in some cases is 
very abundant, as in the Diatoms, Equisetums, and many Grasses, 
but it appears to have but little physiological importance. Its 
chief service seems to be mechanical, affording strength or protec- 
tion to the organ which secretes it. 

Among the other occasional constituents of the ash of plants 
occur Aluminium, Manganese, Fluorine, Bromine, Iodine, Lithium, 
Barium, Strontium, Copper, Cobalt, Nickel, Tin, Zinc, and several 
others, but most of them, when present, exist in very small quan- 
tities. 



CHAPTER II. — FOOD OF PLANTS. 261 

Food of Plants.— The young plant, when it begins to germinate 
from the seed, is still practically dependent on the food-stores laid 
up for it by the parent plant. It is incapable, that is, of deriving 
its sustenance directly from the soil. Its cells, besides containing 
protoplasm, are heavily charged with nourishing matters, such as 
starch, sugar, oil and reserve proteins which the protoplasm makes 
use of for the purposes of growth. It may also, as we have seen, 
have an outside supply laid up for it in the form of endosperm or 
perisperm, which serves the same purpose. When the seed is 
placed in favorable conditions, as when lodged in moist, warm soil, 
the dormant protoplasm of the embryo becomes active, water is 
greedily absorbed by it from the outside, the stores of reserve 
materials are rapidly changed by the aid of ferments present, into 
soluble forms, and these are applied to the formation of new cells. 

As the plant increases in size, sending its radicle into the ground, 
and its plumule, and perhaps also its cotyledons, into the air, its 
food-stores diminish pari passu and are finally exhausted, and the 
plant now becomes entirely dependent on the soil and air for its 
sustenance. In the meantime, it has developed rootlets and numer- 
ous root-hairs as absorbent organs, and expanded to the air a few 
green leaves which are to utilize the absorbed materials. It is 
evident that its food must now be elaborated from the inorganic 
materials. It must, of course, take in the elements mentioned 
above. But it no longer has them supplied in such complex forms 
as those in which they were stored in the seed. On the other hand, 
none of them, save oxygen, can the plant utilize in the elementary 
form; and even its consumption belongs largely, if not wholly, to 
the respiratory rather than to the assimilative process. They are 
absorbed in the form of compounds. Thus the carbon is derived 
from carbon dioxide; the hydrogen, mainly, at least, from water; 
most of the nitrogen from ammonia, ammonium salts and the 
nitrates; the sulphur from the sulphates; the phosphorus from 
the phosphates; chlorine from the chlorides; potassium from its 
phosphate, chloride, sulphate and probably also the silicate; sodium, 
mainly from its chloride, and calcium, magnesium and iron from 
the sulphates, carbonates, nitrates and phosphates of these ele- 
ments. 

The carbon dioxide, made use of by the plant in the elaboration 
of food, is obtained from the air. Oxygen is taken by land plants 
partly from the air, and partly from solution in the water that 
permeates the soil. The mineral salts required by plants exist in 



262 



PART III. — PHYSIOLOGY. 



minute quantities in the dust of the atmosphere, yet in proportion 
large enough to supply the needs of epiphytes; but they occur in 
still greater abundance in most soils, which is the source whence 
the great majority of plants obtain their supplies. Besides these 
inorganic salts there are in most soils various decomposing organic 
matters, which many plants are able to appropriate ; but that these 
are not absolutely essential to plant life, is shown not only by the 

% 




.sZJ^ 



Fig. 492. — Buckwheat plants in water culture. To distilled water in the 
middle jar were added all the mineral salts needed by the plant. To that on the 
left, all except potassium ; to that on the right, all except iron. In the latter 
case, the upper, less shaded leaves are white, not green, in the' plant. (Ganong.) 

fact that Cactus plants and House-leeks grow on bare rocks, 6"r in 
arid sands, but also by experiments like the following: If the root 
of a germinating Bean be placed in a solution containing, in 1,000 
parts of water, about two parts each of potassium nitrate, iron 
phosphate and calcium sulphate, and its leaves be exposed to the 
sunlight and air, care of course being taken that a suitable tem- 
perature be maintained, it will grow nearly, if not quite, as well 
as if planted in the soil. (See, also, Fig. 492.) 

Absorption of Water and Soil Solutions. The great importance 



CHAPTER II. — ABSORPTION OF WATER. 263 

of an adequate supply of water to enable the plant to live and 
grow has already been indicated. The amount needed depends 
upon the species of plant and the conditions surrounding its 
growth. So we have plants which flourish only in moist places, 
others adapted to dry soil; some that do best in the shade, others 
that need sunshine. Temperature and winds also affect the water 
needs of the plant. Unicellular plants and those of few cells can 
absorb water throughout their surfaces; but in larger plants a 
specialization among the cells is necessary and certain exterior 
protoplasts are fitted for the purpose of absorbing water from the 
soil. These cells are chiefly the root-hairs, which are borne just 
back of the growing tip of the root. Root-hairs are cylindrical in 
form and each consists of a single protoplast, surrounded by a 






CI 



^L_ 



Fig. 493. — Root hairs from the root of a mustard seedling. a, in a state 
of turgor; b, the beginning of plasmolysis after immersion in weak salt-solution; 
c, later stage of plasmolysis; n, nucleus. (Gager.) 

delicate cellulose wall. The protoplasts contain sugar solution in 
the vacuoles, and their outer membrane, ectoplasm, presses closely 
against the cell wall. Fig. 493.) 

Having in mind the absolute necessity of water for maintaining 
life and the dependence of all the vital functions upon it, it is 
evident that the process by which water is secured is of great 
importance. It is well known that if two miscible liquids of differ- 
ent densities are placed in contact with each other in such a 
manner as to mingle as little as possible, they will, nevertheless, 
after a short time be found to be uniformly mixed. In the same 
manner a soluble solid when placed in a liquid, without stirring, 
will in the same way diffuse in time throughout the liquid. The 
solution of sugar in water is an example of this phenomenon, 
which is termed diffusion. Gases diffuse in a similar manner. If, 
between the two miscible fluids or two solutions of different densi- 
ties, we interpose a porous membrane, the diffusion proceeds as 



264 



PART III. — PHYSIOLOGY. 



before but the current passes more rapidly from the rarer to the 
denser solution than vice-versa. However, the diffusion continues 
until a condition of equilibrium is established. Such diffusion 
through a membrane is termed Osmosis. (Fig. 494.) 




Fig. 494. An osmoscope, for demonstration of osmosis. The osmotic mem- 
brane is supplied by a parchment-paper cup, whose top is closed by a rubber 
stopper through which is passed a piece of barometer tubing and a funnel with 
stopcock. The cup is filled with molasses and the jar surrounding it with water. 
As osmosis proceeds, the molasses rises in the tube and when it reaches the 
top can be dropped back again by opening the stop-cock of the funnel. 
(Ganong.) 

If a membrane in the form of a small cup or bag of soaked 
parchment is tied , securely on the end of a long piece of glass 
tubing and a solution of sugar is poured into this tube and the 



CHAPTER II. — ABSORPTION OF WATER. 265 

parchment then immersed in a vessel of water, the tube being 
properly supported, a striking phenomenon will be observed; the 
liquid will rise steadily in the tube, against the force of gravity, 
and, if the bag is relatively large and the tube of small caliber, the 
liquid will mount quite rapidly to a height of several feet. Evi- 
dently the rise is due to a strong current from the water into the 
sugar solution, — an illustration of an osmotic process which has 
an obvious connection with the absorption of soil solutions by 
root-hairs as well as the rise of the sap in the stem. It will be 
noted, however, that the intake of the water by the sugar solution 
is accompanied by a slower but discernible outflow of the sugar 
solution into the vessel of water. Herein the osmotic power of 
the root-hair differs from that of the parchment, for the former 
does not lose its sugar to the soil. The explanation is found in 
the protoplasmic lining of the living root-hair which permits the 
passage of water, while preventing the passage of sugar. A mem- 
brane of this kind is called semi-permeable, in distinction from a 
permeable membrane such as parchment. By appropriate chemical 
treatment, semi-permeable membranes may be made artificially, 
which have an osmotic effect closely resembling that of the living 
root-hair. 

The root-hair thus acts in a manner not unlike a pump, 
absorbing water and weak soil solutions by means of its osmotic 
powers and passing this watery liquid on to the conducting tissues 
of the plant, where it rises as sap. It will be noted that the root- 
hairs do not lose their sugar to the sap, for the same reason that 
they do not lose it to the soil, namely, the operation of the semi- 
permeable living membrane, completely surrounding the vacuoles 
which contain the sugar solution. Consideration of the osmotic 
properties of the protoplasts involves not only the production of 
Turgor or fullness, caused by the absorption of water to the fullest 
capacity of the cells, but also the converse condition of plasmolysis 
which is produced when the cell loses its water through contact 
with a denser solution. An illustration of the latter is obtained 
by treating root-hairs or other protoplasts with a five-per cent solu- 
tion of common salt, whereupon the outflow of water occurs more 
rapidly than the intake, since the salt solution is denser than the 
cell sap, with the result that the protoplasmic lining is loosened 
from the cell wall and the protoplasm shrinks and ultimately col- 
lapses. (See also Fig. 493.) 

The absorption of water by the plant is aided in various ways: 



266 



PART III. — PHYSIOLOGY. 



(1) By the branching of the root into numerous fine divisions 
which develop near their tips great numbers of root-hairs. (2) By 
the fact that the root-hairs are in intimate contact with numerous 
earth particles, and even grow fast to them. (3) Each earth par- 
ticle, even when the soil is dry, is enveloped in a closely adhering 
film of water, and as each particle is in contact with adjacent 
ones, the whole virtually forms a complicated network of capillary 
tubes through which water is drawn from a distance, in proportion 
as that adjacent to the root-hairs is absorbed. (4) The liquid of 
the lesser current, from the interior of the cells outward, may be 
of indirect service, on account of its acid properties, in bringing 
mineral matters into solution, which are afterward absorbed by 
the plant. 




Fig. 495. — Diagram to illustrate a root-hair (h) in the soil, and its relation 
to the soil-particles, the capillary film of water (w), and the air spaces (a) ; 
e, epidermal cell of die root, of which the root-hair is an outgrowth, or branch. 
(From Gager, after Sachs.) « 

Ascent of Water. We have already noted that an important 
function of the fibro-vascular bundles is the transportation of sap. 
The water supplied through the' root-hairs, with its weak content 
of soil solutions, is passed inward from the root-hairs and soon 
reaches the tracheal tubes and tracheids which form a part of the 
stele of the root. These water tubes are practically continuous 
"throughout the plant, starting near the tips of the smallest 
branches of the root and extending through the stem and its 
branches into the veins of the leaves, where they finally end in 
the mesophyll. Important factors in the ascent of this watery sap 
are: Root pressure, due to the osmotic action of the root-hairs; 
this continues even after the hairs are so turgid as to be capable 



CHAPTER II. — ASCENT OF WATER. — TRANSPIRATION. 267 

of holding no more water, when pressure exerted by their walls 
forces the water into adjacent cells, from which it streams into 
the water tubes; Transpiration, or the evaporation of water by the 
leaves, in a manner to be discussed presently; Osmotic action of 
the cells of the mesophyll which exerts a pull upon the slender 
water columns in the tubes; and Capillarity, due to the minute 
diameter of the water tubes themselves. 

Transpiration. While a part of the water supplied to the plant 
by its roots is used in development of new parts and in elaboration 
of food, by far the larger amount is evaporated from the leaves 
and the other green parts — a process known as transpiration, since 
it implies the giving off of water in the form of vapor. The 
familiar facts concerning the wilting of leaves and cut flowers 
are instances of the loss of water through transpiration, followed 
by the collapse of the turgid cells and resulting in the loss of the 
rigidity of the soft tissues. The necessity for transpiration is 
evident, for by its aid the protoplasts secure the soluble mineral 
substances required in metabolism and which can enter the plant 
only in very dilute solutions from the soil, and also because only 
through the evaporation of water can the temperature of parts 
exposed directly to the sun's rays be kept within suitable limits. 
A green leaf may often take up many times more solar energy 
than it can possibly utilize in its constructive processes. If this 
energy were allowed to accumulate as heat in the leaf, it would be 
rapidly fatal to the protoplasts. But the heat not employed in 
metabolism is used in evaporating water and the leaf is thus kept 
cool. It is noteworthy that the evaporation of water does not 
take place in epidermal tissues, which, in fact, are especially pro- 
tected against it, but in the intercellular spaces, the exits from 
which are guarded by the stomata and the amount of transpiration 
thus regulated to suit the needs of the plant. 

Gases in Plants. The plant is very largely dependent upon gases 
for the raw material from which its food is made, as well as for 
its respiratory processes. But the very structure which enables 
it to have access to the air, whence these gases are obtained, also 
exposes it to unfavorable conditions of temperature and humidity. 
Hence the need for a special mechanism which may provide means 
of securing the necessary carbon dioxide for photosynthesis and 
oxygen for respiration, while, at the same time, safeguarding the 
transpiration of water. This protective function is supplied by 
the cuticle, a waterproof coating over the epidermis, while the 



268 PART III. — PHYSIOLOGY. 

aerating function is cared for by the stomata and the intercellular 
spaces whose outlets they guard. In older parts of the plant the 
cork answers the purpose of the cuticle; but the pores in the cork, 
the lenticels, though not useless, can scarcely be compared with the 
stomata. The whole substance of the plant is permeated by a 
complete network of intercellular spaces, with some part of which 
every protoplast is in contact. Thus a ready access to the gases 
circulating through the leaf is provided and through the delicate 
cell-walls, constantly kept moist by the water held in the vacuoles, 
these gases, in solution, are supplied to the protoplasts within. 
Not only does the air which fills the intercellular channels contain 
varying amounts of oxygen and carbon dioxide, but it is also well 
charged with watery vapor. 

In the living plant these gases are never absolutely quiescent, 
or in a state of perfect equilibrium. Owing to the metabolic 
activity of the protoplasts, to the evaporation constantly going 
on, to the varying temperature of the air, causing expansion or 
contraction of the gaseous contents of the plant, and to the me- 
chanical agitation caused by the wind moving among the leaves 
and branches, the gases in the plant are in constant movement, 
though the movements are by no means regular or uniform. 



CHAPTER III. 

ELABORATION OF FOOD. — PHOTOSYNTHESIS. — SYNTHESIS OF PROTEINS. 
— DISTRIBUTION AND STORAGE OF FOOD MATERIALS. — DIGESTION. — 
SYMBIOSIS. — RESPIRATION. — GROWTH. — INFLUENCE OF TEMPERA- 
TURE ON THE LIFE OF THE PLANT. — INFLUENCE OF LIGHT ON THE 
LIFE OF THE PLANT. 

Elaboration of Food. It is, as has already been seen, one of the 
functions of living organisms to take in materials different from 
themselves, change them in chemical composition, and appropriate 
them to their uses. Some require that the materials be in a com- 
plex form, others are able to make use of those which are relatively 
simple. Organic beings cannot create energy; they can only dis- 
pense or apply to serviceable ends that which is supplied to them. 
Animals and chlorophylless plants are dependent for their vitality 
on the energy supplied by the oxidation of the complex food-mate- 



CHAPTER m. — PHOTOSYNTHESIS. 260 

rials which they take into their bodies, but chlorophyll plants arc 
able to do an additional work. They can make use of the energy 
of the sun's rays in constructive work. By its aid plants construct, 
from raw materials supplied by the earth and air, complex organic 
matter, which is afterward used, partly by themselves and partly 
by other plants and animals, in carrying on their vital processes 
and building up their tissues. The utilization of the sun's rays 
by the plant is accomplished by the agency of the chlorophyll. 
This green coloring matter, this verdure which in grass and leaf 
gives the chief glory to the summer landscape, has other uses than 
merely to please the eye of man. By means of it, organic beings 
are able to draw perpetual supplies of power from the sun; with- 
out it, it is difficult to conceive how life, save possibly in some of 
its lowest forms, could exist upon the earth. Since this process is 
one of synthesis, the putting together of simpler molecules to 
build up the more complex, and as light is necessary for its accom- 
plishment, the descriptive name Photosynthesis is applied to it. 
It requires not only the presence of light, preferably moderate 
sunlight, but also a suitable temperature, an adequate supply of 
water and free access of air, containing about three parts of carbon 
dioxide in ten thousand, which is the approximate amount usually 
present. Evidently it occurs only in the chloroplasts, for only the 
green coloring matter of these, chlorophyll, has the power of 
absorbing from sunlight certain rays, chiefly red and blue-violet, 
as may be demonstrated by a spectroscopic examination of the 
sunlight that has passed through it. The fact that certain rays 
are thus absorbed gives us some idea of the source of the energy 
which is stored up in the process. 

The precise function of chlorophyll is to apply the energy of 
the sun's rays to the production of some form of carbohydrate, 
which is not starch, but some related body, such as glucose. The 
exact composition of this carbohydrate, we do not know, nor do we 
know precisely the process of its formation, or of the production 
of protein matter from it, but we know it is built up from carbon 
dioxide and water. 

Since the molecules of carbon dioxide and water contain more 
oxygen than is required in the construction of the molecule of a 
carbohydrate, a portion of it escapes from the plant as free oxy- 
gen. Suppose, for example, the carbohydrate be represented by the 
formula C 6 Hi 2 6 we may express the formation of its molecule by 
the following equation: 6CO,+6H,0=C c H 12 Oo+60,. In this case, 



270 PART III. — PHYSIOLOGY. 

it will be seen, six molecules of oxygen, or as much as is contained 
in the carbon dioxide used, become free, and it is evident that an 
amount equivalent to this would be set free in any case, whatever 
the carbohydrate formed. The equation, however, must not be 
taken to express the process which actually takes place, for the 
reactions are probably much more complicated than this would 
imply. A recently advanced hypothesis, which is favored by many 
botanists, suggests that the first interaction is between carbon 
dioxide and water, forming formaldehyde and hydrogen peroxide. 
Immediately following this first step, the formaldehyde is poly- 
merized or condensed by the action of the protoplasm in the plastid, 
while, through the agency of an enzyme in the cell, the hydrogen 
dioxide is decomposed into water and free oxygen. The interven- 
ing stages between formaldehyde and carbohydrates are not under- 
stood; sugar is the simplest substance so far detected and there is 
probably a simple hexose such as glucose. 

The reducing power which the chlorophyll plant possesses is of 
the highest significance, so far as the maintenance of life is con- 
cerned. Animals are continual consumers of oxygen and gener- 
ators of carbon dioxide, and if there were no means of setting free 
again the oxygen they are continually bringing into combination, 
the atmosphere would soon become poisonous and unfit to sustain 
animal life ; but plants, by feeding upon the carbon dioxide which 
animals exhale, and restoring the oxygen which they consume, 
maintain the atmosphere at nearly a constant composition, and the 
balance of life is kept in equilibrium. 

An interesting calculation based on the foregoing equation, 
indicates that for the production of one gram of glucose, 750 cubic 
centimeters of pure carbon dioxide are required and that this 
amount is normally present in two cubic meters of air. And the 
same volume of pure oxygen will be released. It has been further 
estimated that 750 cubic centimeters of carbon dioxide are used by 
a square meter of green leaf each hour on a bright summer day. 
On this basis and allowing for the cessation of photosynthetic work 
at night and during the winter, it has been calculated that it re- 
quires about 150 square meters of leaf at work during the summer 
to balance the respiration of a man for a year. 

Attention has already been called to the fact that starch is the 
first visible product of photosynthesis and that it occurs in the 
chloroplasts during the height of the photosynthetic process and 
can be detected by the employment of iodine solution, which turns 



CHAPTER III. — SYNTHESIS OF PROTEINS. 271 

it blue (see Fig. 496). Since the formation of sugar precedes 
that of starch and since an excess of sugar in solution in the cell 
sap interferes with the activity of the chloroplasts, it would appear 
that starch represents the production of carbohydrates in" excess 




Fig. 496. — Accumulation of starch in the illuminated portion of a leaf. The 
light-colored portion was shaded by tinfoil and the starch has been stained by 
iodine. (Palladin.) 



of the immediate requirements of the protoplasts and that, stored 
in this insoluble form, it permits the photosynthetic action to go 
on freely while other conditions are favorable. Starch, then, is to 
be regarded as stored carbohydrate, wherever it appears. It is one 
of the most important of the reserve food-materials of the plant. 
Stored away in various parts of the vegetable structure, it is so 
much capital which the plant may draw upon in case of need, to 
build up new tissues, to repair losses and wastes, or to carry on 
the exhaustive work of reproduction. 

The power to utilize starch for the building up of the tissues 
is not the exclusive property of the green cells, as is that of the 
first formation of carbohydrate, but it is possessed to a greater or 
less extent by all the living cells of the plant. Tissue construction 
from starch is also not dependent upon light. A potato will sprout 
in a dark cellar, and the sprouts will continue to grow until they 
have exhausted all the reserve food-materials in the tuber; but 
when this is done they die, for they cannot, without the aid of the 
sun's radiant energy, construct new materials; no new carbo- 
hydrate can be formed, as we have seen, in the absence of light. 

The Synthesis of Proteins. Proteins contain nitrogen, which 
carbohydrates lack. While nitrogen exists in abundance in the 
elemental form, which constitutes four-fifths of the atmosphere, 



272 



PART III. PHYSIOLOGY. 



yet plants, with possibly few exceptions, cannot utilize or "fix" 
the free nitrogen of the air but require that it be supplied to them 




Fig. 497. — Longitudinal section through Red Clover rootlet, showing tubercle 
formation due to the root nodule microbe, Rhizobium mutabile. The tubercle is 
only partially developed, a, root hairs. These do not develop on the nodule, 
b, the normal root parenchyma, c. vascular tissue, d, infected area, also show- 
ing the infecting strands. The cells are filled with bacteria. e, apical areas, 
the growing areas of tbe tubercle. (Schneider.) 



CHAPTER III. DISTRIBUTION AND STORAGE OF FOOD. 273 

in combination in the form of nitrates, — chiefly the nitrates of the 
alkalies or alkaline earths. Green plants use best the nitrates of 
potassium or calcium; fungi prefer ammonium nitrate. Of two 
groups of nitrogen-fixing bacteria, Nitrosomas changes ammonia 
into nitrites, while Nitrobacter ©xidizes nitrites into nitrates. The 
bacterium-like organisms found in the root nodules of the Legu- 
minosae are able to fix the nitrogen of the air so that it may be 
utilized by the plant. (Fig. 497.) 

We know but little of the synthesis of proteins. Evidently it 
is independent of the synthesis of carbohydrates, for the fungi, 
though lacking in chlorophyll, are able to grow and thrive in media 
containing carbohydrates and certain ammonia salts but destitute 
of proteins. Apparently light is not necessary to protein construc- 
tion, which may, therefore, take place in the protoplasts of any 
part of the plant. The plant is able to store up a reserve supply 
of proteins, just as of other food products, and to utilize these for 
food when occasion arises. 

As with proteins, so with fixed oils and fats, we know that 
these are important reserve foods of the plant but we know little 
or nothing of the manner of their formation. Presumably, they 
are formed in the protoplasts from starch and therefore, indirectly, 
from glucose. 

The Distribution and Storage of Reserve-Materials. The manu- 
facture of plant food, whether carbohydrate, protein or fat, goes 
on, under favorable conditions, in excess of the immediate needs 
of the plant and results in the storage of a reserve supply in 
various parts, such as fleshy underground stems and roots, seeds, 
the medullary rays and middle bark of stems, and the region 
adjacent to the buds. In the histological part of this book we 
have already considered these various kinds of food reserves. They 
must be transported in solution from the protoplasts where they 
were formed, to those where they are to be stored. Thus the 
starch granules formed in the chloroplasts under the influence of 
light, undergo solution in darkness, and disappear. Probably this 
solvent process is in continual operation during the day, but, 
owing to the fact that the formation is more rapid than the solu- 
tion, the latter process cannot be directly observed. In under- 
going solution, the starch is changed into sugar, which, in its 
various forms, is a highly diffusible substance. It may thus be 
conveyed to parts very remote from its place of formation. The 



274 



Part hi. — physiology. 



transformation is brougnt about by the agency of diastase, or some 
similar ferment. 

In the form of sugar, it may be conveyed to growing parts 
and applied to the construction of tissues, or it may be carried to 
various parts of the plant, as seeds, tubers, etc., and laid by as 
reserve material. In this case it is sometimes stored as sugar, 
for example, in the Sugar Beet; sometimes it is laid up in the 
form of cellulose, as in the Ivory Palm (Fig. 498) and Nux Vomica; 




Fig. 498. — A section through the horny albumen of a seed, showing walls 
thickened by a deposit of cellulose which later is used as food for the seedling. 



sometimes it goes to the formation of reserve proteid material, 
such as aleurone grains, etc.; but it is more commonly either 
re-converted into starch, or else stored in the form of fixed oil. 

When starch, fats or proteins are to be conveyed from the tis- 
sues where they are held in reserve to growing parts, they are 
again brought into solution by the agency of a ferment. 

This process is digestion just as truly as that of animals, 
though in plants occurring within the cell only. However, the 
glands of insectivorous plants such as Sundew, Venus' Fly Trap 
and the Pitcher plants closely parallel the action of the alimentary 
tract of animals. When food has been digested, it is not yet a 
part of the living material of the plant, but must still be assim- 
ilated or incorporated into the living protoplasm. Concerning this 
assimilation we know but little, for although digestion can be car- 



CHAPTER III. — SYMBIOSIS. 275 

ried on in a test tube and even carbohydrates can be produced 
artificially, no one has yet succeeded in producing protoplasm syn- 
thetically. Only living protoplasts are able to accomplish this. 
The dictum, "Omne vivum e vivo" (All life from life) still holds. 
Of the food thus assimilated, a part is subsequently employed to 
furnish energy, through the process of respiration, a part is trans- 
formed into plastic materials for the construction of the cell walls, 
a part goes to form various cell contents and secretions, and a 
part remains as protoplasm itself. 

Symbiosis or Mutualism. While green plants are fully equipped 
to elaborate their own food, many do not depend entirely on their 
photosynthetic mechanism but supplement it to a greater or less 
extent, or even replace it altogether, by securing elaborated food 
from their neighbors or their surroundings. Saprophytic plants 
obtain their food from partly decomposed or decaying animal or 
vegetable matter in the soil. Chlorophylless plants are sapro- 
phytes, except a few that are parasitic in habit, and most chloro- 
phyll bearing plants make use of decomposed organic material in 
the soil to a considerable extent; hence the importance of manures 
and fertilizers, especially to young and rapidly growing plants. 
It has been shown that not only nitrogenous compounds but even 
carbohydrates can be absorbed from the soil by green plants. 

Parasites absorb food from another plant, termed the host 
plant. The Dodder is a familiar example. It develops no foliage 
leaves and forms no chlorophyll. The Mistletoe is typical of an- 
other group which are only partly parasitic, as they form chloro- 
phyll and bear green leaves. In fact, it has been pointed out that 
the Mistletoe, remaining green in winter, actually supplies food 
to its host during the period in which the latter, having lost its 
leaves, is unable to supply itself. A similar arrangement exists 
among other green plants, Castilleja and Comandra are instances 
of it; both are parasitic on the roots of other plants (semi- 
parasites). The close physiological association of two plants to 
their mutual advantage is well illustrated in the lichens, com- 
posite plants of fungi and algae. The alga, having chlorophyll, 
supplies the food and is held in a sort of slavery by the fungus. 
Such arrangements are termed symbiosis and the plants concerned 
symbionts. An interesting example is also afforded by certain 
fungi which live symbiotically with the roots of forest trees and 
of other highly-organized plants, forming a felt-like mass of 
fungal filaments around the epidermis of the root or even pene- 



276 PART III. PHYSIOLOGY. 

trating the latter and ramifying through its tissues. (Fig, 499.) 
Such Mycorhizas are found chiefly in soils rich in humus, and the 
fungal hyphse answer the purpose of root hairs, especially in 
securing for their host the organic compounds of the humus. The 
nitrogen-fixing bacteria, already mentioned, afford further exam- 
ples of symbiosis. The subject is of great and increasing economic 
importance. 

Respiration in plants, as in animals, consists essentially in the 
oxidation of organic materials, whereby complex molecules are 




Fig. 499. — Epiphytic mycorhiza of Fagus sylvatica. (A) twice magnified; 
(B) tip of root partially denuded of the investing mantle (x30). (Pfeffer.) 

broken down to simpler forms and energy is released. The organic 
materials consumed in this process are known as foods, a term 
which is by some extended to include the mineral salts, and even 
water, since these are needed for the growth and repair of plants. 
In a more restricted sense, however, foods are comparable to fuel, 
and like the latter, supply, through oxidation, the energy needed 
to maintain the vital processes of the plant. This form of de- 
structive metabolism, though often overtopped and largely con- 
cealed by the photosynthetic operations is, nevertheless, just as 
necessary to the life of the plant as it is to the animal. In both 
animals and plants the end-products of respiration are carbon 
dioxide and water, which, in the plants, may be given, off through 
the intercellular canals and the stomata, or may be used at once 
in the converse process of photosynthesis. While this exchange of 
gases is analogous to the breathing of animals, it is well to dif- 



CHAPTER III. — RESPIRATION. — GROWTH. 277 

ferentiate between the two, recognizing that plants have no 
mechanism comparable to the lungs of animals, and restricting the 
term respiration to the process carried on in every living proto- 
plast. 

Respiration is evidently a chemical process, but a complex 
one. The oxygen does not unite immediately with the organic 
material, as in combustion, but is first absorbed in aqueous solu- 
tion by the protoplast and acts through its agency, with the assist- 
ance of an oxidizing enzyme. The actual liberation of energy in 
the protoplast is very gradual, and while partly manifested as 
heat and thereby serving to maintain the normal temperature of 
the plant, it is chiefly employed in the series of transformations 
which constitute the processes of metabolism already discussed. 
Not all respiration requires the presence of oxygen, for certain 
bacteria and fungi secrete a ferment w r hich can break down com- 
plex organic compounds, rich in oxygen, with the release of energy 
and the formation of carbon dioxide and water. Such decomposi- 
tion is termed anaerobic, for air is not necessary for its mainte- 
nance. Both serobic and ancerobic kinds of respiration are forms 
of fermentation and depend upon the action of enzymes, as already 
stated. 

Growth is the increase in size and substance, either of the whole 
plant or of any of its parts. It comprises three phases; first, the 
formation of new parts; second, the enlargement of these new 
parts to their full size; third, the ripening of these parts for their 
functions, whatever they may be. Growth goes on during the 
entire life of the plant, in at least some of its parts. Thus a tree 
continues to put forth leaves and new stems so long as it lives, 
even though it may not noticeably increase in size. At times, even, 
the growth of one part may cause decrease or loss at another 
place, as shown by the sprouting of potatoes or other fleshy under- 
ground stems, where the reserve food supply is consumed and the 
storage tissues depleted to enable the sprouts to be formed. While 
in the simpler and smaller plants, growth may occur throughout 
the plant at one time, in the larger and more complex structures 
the growth is confined to certain regions known as growing points. 
Here, new cells are formed through cell division, and this increase 
in the number of cells, constituting the first phase of growth, is 
succeeded by the enlargement of the new cells, illustrating the 
second stage, which, in turn, is followed by the thickening of their 
walls and the secretion of certain substances in the protoplasts, 



278 PART III. — PHYSIOLOGY. 

fitting them for their work in the plant, and constituting the third 
stage of growth. 

In order that the cell may grow it must be supplied with 
nutritive materials, with which to increase its substance as well 
as to consume in furnishing the needed energy; it must have 
a sufficient amount of oxygen, for respiration is necessary for 
the release of energy; it must have an adequate supply of 
water, for only turgid cells can grow; it must possess or form 
osmotic substances within the cell, for osmosis is necessary to 
turgor and therefore to growth, and finally, it must have the 
proper amount of heat, for the chemical changes constituting 
metabolism take place only within certain ranges of temperature. 
When these conditions are met, the young cell, formed at one of 
the growing points, osmotically absorbs water containing nutritive 
materials in solution, and the resulting hydrostatic pressure 
stretches the cell wall, which is rapidly added to by the deposit 
of new wall material secreted by the cytoplasm. Meanwhile the 
cytoplasm increases in amount, and thus keeps pace for a time 
with the growth of the cell, but, presently, vacuoles form in it and 
are filled with sap. By the time the cell has reached its full size 
the vacuoles occupy the larger part of it and the cytoplasm is 
restricted chiefly to the living film lining the wall. The cell wall 
usually continues to increase in thickness after its growth in area 
has ceased. 

Growth is not uniform in rate; it commonly begins slowly, 
gradually accelerates its speed and then slows down until it 
ceases. These changes in growth constitute what is called the 
"grand period," and are noticeable not only in the cells, but in 
the larger structures, roots, stems and other plant organs as well. 
Thus, in roots, the new cells at the growing point (primordial 
meristem) divide soon after they formed, but those farthest from 
the apex gradually cease to divide and then pass through the 
stages above outlined, at length becoming a part of the permanent 
tissues, in which the power of further growth has been lost. 
Finally, growth in different cells, tissues or organs of the plant is 
not uniform. The unfolding of leaves from the bud, the twining 
of stems and the curving of other parts, is directly due to such 
unequal turgidity or growth, which will be discussed in connec- 
tion with movements of plants. 

Influence of Temperature on Growth. The vital processes of the 
plant can only go on within certain limits of temperature. If it 



CHAPTER III. — INFLUENCE OF TEMPERATURE AND LIGHT. 279 

be too low, the seed will not germinate or the bud unfold, and if it 
be increased beyond certain limits, life is at first suspended and 
then destroyed. For each species of plant there is a minimum 
temperature below which activity ceases, an optimum temperature 
at which its activities are greatest, and a maximum temperature 
which cannot be exceeded without stopping the vital processes. 
These temperatures differ for different plants. Some, as the Red- 
snow plant of the Arctic regions, thrive at a temperature very 
near the freezing-point, while others, as the Vanilla plant, cannot 
flourish except in the tropics. 

A very low temperature as well as a very high one may cause 
the death of a plant, but the facility with which it is destroyed 
by either will depend upon the amount of water in its tissues. 
Dry seeds and spores have in some instances been found to endure 
an extremely low temperature without destruction of their vitality, 
while the vigorously growing plants of the same species were 
unable to endure even a slight frost. Similarly, a seed will endure 
a temperature many degrees higher than will the actively growing 
plant which springs from it. 

It seems evident that when plants are killed by frost, it is on 
account of the formation of ice crystals by the withdrawal of 
water from the protoplasm, thus seriously disturbing the equi- 
librium of the protoplast, and probably setting up destructive 
chemical changes. The life of a plant that has been frozen may, 
however, often be saved by thawing it very slowly, when if rapidly 
thawed it would perish. Much, though, depends upon the habit 
of the plant. The fact that physical and chemical changes are 
promoted by heat and that these changes constitute the metabolism 
of the plant but are controlled by the living protoplasm, no doubt 
accounts for the importance of heat as a factor in growth. Few 
actively growing plants can endure a temperature higher than 
122° F. Most of them grow best at a temperature of about 85° F. 

Influence of Light on the Life of the Plant. It has already been 
shown that green plants are dependent on light for their photo- 
synthetic power, and as all other organisms are dependent, in the 
long run, on the work done by green plants, light is indirectly 
essential to all life. Those organisms, however, which do not con- 
tain chlorophyll are not directly dependent upon light, hence may 
thrive in darkness. Give a fungus the decaying organic matter 
on which to grow, and it will flourish in the blackness of the 
deepest recesses of a cave. Even those cells of the chlorophyll 



280 PART III. PHYSIOLOGY. 

plant which do not contain green coloring matter are able to dis- 
charge their vital functions in darkness as well as in the light. 
Light is essential only to the construction of organic out of inor- 
ganic matters; it is not necessary for carrying on the oxidizing 
changes that take place in the plant. A seed will germinate in 
absolute darkness, but the seedling will cease growing and perish 
as soon as it has exhausted the nutrient matters which were stored 
up for its use. A potato tuber permitted to grow in a dark cellar 
will apparently make a very vigorous growth, but when the shoots 
have exhausted all the nourishment stored up in the tuber, growth 
ceases, and if a comparison be made between the dry weight of the 
tuber at the beginning, and that of the sprouts and exhausted 
tuber at the close of the experiment, it will be found that there 
has been no increase; no new material has been added. More- 
over, in plants thus growing in darkness, chlorophyll very rarely 
develops ; both leaves and stem have a blanched appearance instead 
of the normal green. 

Indeed, it is a matter of common observation that plants often 
grow more at night than during the day. In rapidly growing 
plants, such as cucumbers or melons, this is especially noticeable 
after a warm summer night. Not only do plants in semi-darkness 
"reach out" toward the light and thereby lengthen their stems, 
but at night photosynthesis ceases and the plant can devote its 
energies entirely to growth. Again, an excess of light, like an 
excess of heat, may injure the plant, and the amount of light best 
suited to the growth of the plant varies with the species. Hence 
we have shade-loving plants, and for the successful cultivation of 
some of our valuable crops, such as Tobacco, as well as for Golden 
Seal and Ginseng, the grower must provide artificial shade. 

Light, also, by influencing the growth of the plants, or by the 
stimulant effects it exerts upon the living matter of their cells, 
gives rise to certain movements; but these may be more appro- 
priately considered under the subject of the movements of plants, 
which will be taken up presently. 



CHAPTER IV. 



MOVEMENTS OF PLANTS. — LOCOMOTION. — GEOTROPISM. — HELIOTRO- 
PISM. — IRRITABILITY. — REPRODUCTION OF PLANTS. 

Movements of Plants. Although some plants, like the so-called 
Rose of Jericho, wither during the dry season and are blown by the 



CHAPTEB IV. — MOVEMENTS OF PLANT.-. 281 

wind, often to great distances over the sandy plains, but resume 
their verdure and send forth blossoms when they reach moist soil, 
or at the advent of the rainy season, strictly spontaneous move- 
ments of transition or locomotion are confined, as we have already 
stated, to the flowerless plants, and are most conspicuous among 
the lowest forms. They are exhibited chiefly by isolated cells, or 
by small colonies of cells. This is not because the protoplasm of 
higher plants has really less activity, but rather because it is 
mainly confined within rigid walls, so that the young and growing 
parts, or those, at least, in which the cell walls are thinnest, are 
the only ones free to move. 

Locomotion in plants exists under several modifications, the 
amoeboid, the ciliary, and a creeping motion of ill-defined character, 
such as that observed in many Diatoms, Desmids, etc. Plants that 
exhibit amoeboid movements are unicellular and destitute of a 
cell-wall. The movement is a slow, creeping one, accompanied by 
constant changes of form, or the throwing out of processes resem- 
bling the pseudopodia of Rhizopods. It is undoubtedly the most 
primitive form of locomotion, and is exhibited only by the simplest 
living forms, or by more complex ones in the earlier stages of their 
development. It is illustrated in the Myxomycetes, Fig. 506. 

Ciliary motion is accomplished by means of delicate hair-like or 
lash-like projections of the protoplasm, called cilia. In these 
organs, the ordinary protoplasmic contractility has acquired a high 
degree of development to suit them to the functions of locomotion, 
and by their rapid bending to and fro, the cell to which they are 
attached is propelled through the water in which it lives. While 
amoeboid movement is slow and creeping, this is conspicuous for 
its rapidity, and is to be regarded as a higher development. It is 
observed in many mature plants belonging to the lower orders, 
examples of which are illustrated in Fig. 513 and in the repro- 
ductive spores of the great majority of flowerless plants. See 
Figs. 505, 527, 539, 594. 

Movements not Locomotive. First to be noticed among these 
are the movements of the cytoplasm within the cell. In some cells, 
for instance those of the stems and leaves of Chara and Nitella, 
the leaves of Vallisneria, many hairs, such as the stinging hairs 
of the Nettle, those on the filaments of Tradescantia, etc., the phe- 
nomena are conspicuous, and there are few things more wonderful 
than to watch them under the microscope. Though movements 
are more obvious in these examples, there is no doubt that they 



282 PART III. — PHYSIOLOGY. 

take place more slowly in all living cells. As regards their nature, 
they are streaming movements in the bands and plates of cyto- 
plasm that cross the cell, or gliding movements of the great mass 
of the cytoplasm around the interior of the cell, or sometimes 
crossing from one wall of the cell to the other. In cells containing 
chloroplasts the latter very commonly assume a different position, 
in strong light, from that which they occupy when the light is 
greatly diminished. These changes of position are due to the 
movements of the cytoplasm in which they are imbedded. In 
strong light they ordinarily gather along the side walls of the cell, 
or those which are perpendicular, or nearly so to the surface of 
the organ, while in dim light or darkness they congregate along 
the outer and inner walls. In Fig. 500, a is a cell from the spongy 





Fig. 500. — Cells of the lowermost layer of spongy parenchyma from the leaf 
of Oxalis Acetosella, seen in a direction at right angles to the surface of the 
leaf, a, plane position of chloroplasts in diffused light ; b, profile position after 
short exposure to the sun; c, position after longer exposure to the sun. (After 
Sachs and Stahl.) 

parenchyma of the leaf 'of Oxalis acetosella that has been exposed 
to weak or diffused daylight; the chloroplasts are nearly evenly 
distributed along the walls parallel to the surface of the leaf. 
b shows a similar cell from a part of the leaf which has been 
exposed for a short time to direct sunlight; the chloroplasts are 
here seen distributed along the walls which lie perpendicular to the 
epidermis, c shows the position of the chloroplasts in a cell which 
has been exposed for a longer time to direct sunlight. They are 
now massed together along the walls perpendicular to the surface 
of the leaf. 

Geotropism. By this is meant those movements of growth, the 
direction of which is determined by the stimulus produced by 
gravity on the growing organs. It has been ascertained by plant- 
ing a germinating seed on the rim of a wheel which was made to 
rotate in a vertical plane with a velocity sufficient to produce a 



CHAPTER IV. — GEOTROPISM. — HELIOTROPISM. 283 

considerable centrifugal pull at the circumference, that the stem 
grew inward toward the center of the wheel, or in a direction 
opposed to the pull, while the root grew outward from the center, 
oi- in the same direction as the pull, indicating that in the ordinary- 
growth of plants, gravity is the cause of the downward trend of 
the root, and also that of the upward trend of the stem. This 
conclusion is confirmed by other experiments. The condition of 
the growing tissues of the root is such that when that organ is 
stimulated by a constant downward pull it grows downward, while 
the different condition of the tissues of the stem causes that organ 
to grow in the opposite direction under the influence of the same 
stimulus. Under ordinary conditions, other forces, as we shall 
presently see, more or less modify the action of gravity; still it is 
mainly this which determines the position of the various organs of 
the plant with respect to the horizon. It is not only the chief cause 
of the downward growth of the main root of a tree, and the 
upward growth of the stem, but it has much to do with the hori- 
zontal or oblique growth of the branches and leaves, and if any 
young and growing organ be by any cause diverted from its 
wonted direction, it tends to resume its normal direction again 
when the disturbing cause is removed. An organ which grows 
directly downward or in the direction^ of the pull of gravity is 
said to be positively geotropic; one which grows directly upward, 
or in opposition to that pull, is said to be negatively geotropic, and 
one which assumes a position at right angles, or nearly so, to the 
pull is said to be transversely geotropic. (Fig. 501.) 

Heliotropism or phototropism includes movements caused by 
the stimulant effects of light. The effect may be either to cause 
the organ to curve toward the source of light, or to bend away 
from it. In the former case the plant or organ is said to be posi- 
tively heliotropic, and in the latter, negatively heliotropic or aphe- 
Uotropic. Plants growing in the open sunshine of course always 
have one side more strongly illuminated than the other, but owing 
to the diurnal motion of the earth, the effect of which is to cause 
the direction of the light to constantly change, and owing also to 
the slowness with which most organs respond to the stimulus, 
movements of this character are not ordinarily conspicuous. It 
would not be difficult to prove, however, that the position which 
leaves and some other organs assume is due in part at least to the 
stimulant effects of light. In the case of a few plants, like the 
sunflower, when they are young and actively growing, the sensi- 



284 



PART III. — PHYSIOLOGY. 



tiveness to light is so great that the leaves and stem follow the 
sun during his daily course. When, however, we cultivate a plant 
in such a Way that it receives its light chiefly from one direction, 
as for example when a house-plant is grown in a window, helio- 




Fig. 501. — Experiment to demonstrate positive geotropism in the root of a 
seedling of Lupine (Lupinus albus). S, metal stand; P, Petri dish, with edges 
lined with moist filter-paper. The seedling is pinned to a strip of sheet cork. 
The four views are of the same seedling at the successive hours as indicated. 
(Gager.) 



tropic movements are very noticeable. The stems, branches and 
petioles bend over toward the more strongly illuminated side, and 
the leaf-blades place themselves in a plane at right angles to the 
rays which fall upon them. If a seedling plant of almost any kind 
that has an erect habit, be fastened upright in a glass of clear 
water and placed in a window so that one side is presented toward 
strong light and the other toward darkness, in a few hours the 
stem will be bent perceptibly toward the light and the root away 
from it. The utility of these movements in enabling the plant to 
adjust the position of its organs in such a manner as to make 



CHAPTER IV. — HYDROTROPISM. — CIRCUMNUTATION. 285 

them of the greatest service, is clearly evident. It is not always 
the case, however, that homologous organs behave alike under the 
same stimulus. The young shoots of the Ivy, when grown in a 
window, bend away from the light instead of toward it. But here 
also the movements are of advantage to the plant in enabling it 
to bring its rootlets into contact with walls, tree- trunks, etc., and 
so to climb. The negatively heliotropic movements of the rootlets 
of this and other root climbers, and of the tendrils of the Virginia 
Creeper and a few other climbers, subserve the same end. 

But movements of heliotropism are not confined to multicellular 
organs; they are often observed in organs composed of a single 
cell, or even in unicellular plants. The root-hairs of many plants, 
for example, are negatively heliotropic, while the spore-bearing 
hyphae of some molds are positively so, and if certain minute 
Algae, such as Desmids, which are endowed with the power of loco- 
motion be placed in a glass of water having one side exposed to 
strong light and the other to comparative darkness, it will be 
found, after a time, that the Algae have accumulated on the illum- 
inated side of the glass. 

Experiment proves that the rays most concerned in producing 
heliotropic movements are those toward the violet end of the 
spectrum. 

The phenomena of heliotropism are similar, in all essential 
respects, to those of geotropism, except that the force which causes 
the movement is light instead of gravity. In the one case it is the 
direction of a pull, in the other the direction of an ether vibration, 
which, acting upon the irritable living matter of the cell, brings 
about changes that cause the organ to place itself in a different 
position. 

It has been found also that movements are sometimes produced 
by the ultra-red or dark heat rays of the spectrum, some organs 
moving toward the source of heat, and others away from it. The 
phenomenon is called thermotropism. 

Hydrotropism is a term applied to organs which, like young 
roots, have been found to curve toward a moist surface. It is a 
source of great advantage to a plant, since, by means of it, its 
roots are, so to speak, able to seek out the moisture and avoid the 
dryer and ordinarily less nutritive portions of the soil. (Fig. 502.) 

Circumnutation. This term was first applied by Darwin to the 
revolving movements observed in the tips of the young and grow- 
ing shoots, roots and leaves of the higher plants. The movement 



286 



PART III.— PHYSIOLOGY. 



consists in a bowing of the organ successively to all points of the 
compass, thus causing its tip to describe a figure approximating 
a circle, or, more commonly, an ellipse. It is caused by the forma- 
tion, lengthwise of the organ, of a line of growth which travels 
laterally around the organ. 




Fig. 502. — An experiment to show the effect of moisture upon the direc- 
tion of the growth of roots. The box containing moist sawdust in which the 
Corn is planted has a bottom of wire netting. After the roots grew through 
the meshes, thus coming in contact with dry air. they changed their direction 
and grew along the bottom of the box, thus keening in contact with moisture. 
(Martin.) 



The circumnutating movements of the growing radicle doubt- 
less aid it in penetrating the soil; those of the upper internodes 
of twining plants are the means by which they climb; the corre- 
sponding movements of some other climbers constitute an efficient 
means by which they are able to bring their climbing organs — 
rootlets, sensitive petioles or tendrils — into contact with a sup- 
port, and so secure a hold by which they may raise themselves 
toward the sunlight ; and the tendrils themselves are also commonly 
endowed with circumnutating movements which serve the same 
useful purpose. This is the most important of all the plant move- 
ments. It is also regarded by Darwin as the fundamental form, 
of which the others are modifications. The phenomena of geotrop- 
ism, heliotropism, etc., are caused by the modification of this 
primitive form by external stimuli of various kinds, as gravitation, 
light, heat, etc. 

Nyctitropic, or Sleep Movements. The leaves of Oxalis, of 
Clover, of the Acacias, and the compound leaves of many other 
plants, have been observed to assume positions quite different at 
night from those they occupy during the day. See Figs. 503 and 



CHAPTER IV. — SLEEP MOVEMENTS. 



287 



504. By day the leaflets are expanded so as to expose as large a 
surface as possible to the light, but at night they droop and become 
pendant from the axis on which they are borne, or, in some 
instances, fold together so as to present to the sky as little surface 
as possible. These movements are serviceable to the plant in pre- 
venting excessive radiation of heat at night. In many plants the 
combined upper surfaces of the leaves amount to an enormous 




Fif. 503. Fig. 504. 

Fig. 503. — Leaf of White Clover with the leaflets in their diurnal position. 
Fig. 504. — Leaf of White Clover with leaflets in the position which they 
assume at night. 



total, and if this be spread out to the sky, on a clear night, the 
loss of heat by radiation must be very great — so great, in fact, 
that serious injury to delicate tissues would often result, especially 
in the case of plants inhabiting dry regions, or open plains. Experi- 
ment has proved that when the leaves of nyctitropic plants are 
pinned out horizontally, so that they cannot close, they do suffer 
injury from this cause, the leaflets often turning brown and dying 
after a night's exposure. 

The cotyledons of many germinating seeds of dicotyledonous 
plants exhibit nyctitropic movements in a conspicuous manner. 
Sometimes they droop at night like the leaflets of Oxalis, while in 
other cases they rise from the horizontal to the vertical position, 
closing over the plumule, and thus protecting it, as well as theii 
own upper surfaces. 

The flowers of many plants also show similar movements 
Some open in sunshine and close at night, or in cloudy weather; 
others, like the Evening Primrose and the White Lychnis, have 
the opposite habit of opening by night and closing by day. Some 



288 PART III. — PHYSIOLOGY. 

/ 

flowers have very regular hours of opening and closing; for exam- 
ple, according to Linne and De Candolle, the Purple Morning-glory 
opens at 2 a. M.; the White Water-lily at 7 a.m.; the Blue Passion- 
flower at 12 M.; the common Evening Primrose at 6 P. M., and the 
Night-blooming Cereus between 7 and 8 P. M. Sometimes the 
movements appear to be dependent on variation in the intensity 
of light; at others they seem to be quite independent of it, as in 
the case of the Goat's-beard (Tragopogon pratensis) , which opens 
in the morning and closes at or before noon. 

The opening and closing movements of the floral organs are 
accomplished, like those of ordinary leaves, by unequal growth, 
or, sometimes, mainly by unequal turgescence of the upper and 
under surfaces of each organ, or of its basal portion. 

So far as the utility of these floral movements are concerned, 
they mostly have reference in some way to cross-fertilization. The 
closing of a flower at night, or when the sky is darkened at the 
approach of a storm, serves to prevent the wastage of its nectar 
and pollen by dew and rain, and the closing at night, in some cases 
at least, prevents the access of night-flying insects that could not 
be serviceable to the flower in cross-fertilization, while in the 
reverse case of flowers that open by night and close by day, they 
are mostly adapted to cross-fertilization by night-flying insects, 
and it is an obvious advantage to them to protect themselves, by 
closing, from unserviceable day-flying insects. 

Besides these, there are other more conspicuous movements 
observed in some plants, the use of which is not so well under- 
stood. The Telegraph Plant (Desmodium gyrans) , a native of 
India, affords a conspicuous example. The plant has compound 
leaves, with the leaflets in threes, two small lateral ones, and a 
much larger terminal one. The lateral leaflets are in constant 
motion, sometimes moving up and down, and sometimes circularly. 
The motions are often rapid, particularly in bright sunshine, and 
they are frequently unequal and jerky. 

These movements, as well as those described as nyctitropic, are 
also to be regarded as modifications of circumnutation. 

Irritability. Attention has already been called to various phe- 
nomena under this head, such as the sensitiveness to contact shown 
by the leaves of the Sensitive Plant, by those of Venus' Fly-trap, by 
the stamens of the Barberry, etc. Phenomena like these are by 
no means exceptional, though in many cases much less conspicuous. 
In fact, all the spontaneous movements of plants that have been 



CHAPTER IV. — IRRITABILITY. 289 

described are evidences of irritability. They take place, that is, 
in response to a stimulus of some sort communicated to the living 
protoplasm. The irritant or stimulant influence may be gravity 
tion, light, heat, chemical agents, electricity, or mechanical shock, 
pressure or contact. 

If we experiment upon a mass of naked, living protoplasm, 
such as, for example, the Plasmodium of one of the Myxomycetes, 
we find that a shock causes it to contract, whether the shock be 
that produced by a mechanical blow, or that caused by a current 
of electricity. Also, if we strike a young and growing shoot a 
smart blow, it will respond to the stimulus by slowly bending, the 
character of the movement it undergoes depending on the force 
and direction of the blow. Facts like these, and numerous similar 
ones, justify the conclusion already stated, that irritability is a 
property common to all living protoplasm. 

Among the more interesting phenomena of this kind are the 
sensitiveness of tendrils and other climbing organs. Take, for 
example, the tendril of the Passion-flower. When young, it is 
straightened out and somewhat hooked at the apex, and is carried 
around in a circle by circumnutating movements. If, in the course 
of these, it fails to be brought into contact with an object suitable 
for it to cling to, it soon coils up into a close spiral, loses its sensi- 
tiveness, and finally withers away. But if the hook at its extremity 
comes into contact with the stem or branch of another plant or 
other suitable object, it is likely to catch upon it, the irritation of 
the contact causes it to bend around it and clasp it firmly, ulti- 
mately, if the shape of the object permits, forming two or three 
coils about it. The rest of the tendril then forms a double spiral, 
a part of which winds in one direction, and the rest in the opposite 
direction, and at the same time its tissues acquire great firmness 
and elasticity. The spiral coils thus formed serve the double use 
of drawing the plant closer to its support, and of acting as a spiral 
spring to prevent it from being torn away by a sudden strain, such 
as that produced by a gust of wind. 

The tendrils of some species of Ampelopsis, as we have seen, 
are apheliotropic, and by virtue of this property, and since walls, 
tree-trunks, etc., are nearly always less strongly illuminated than 
the sky, they bend toward such surfaces. If they are able to reach 
them, the sensitive tips of the branches are irritated by the con- 
tact, and they enlarge, become flattened into sucker-like discs, 
which, by means of a cement they secrete, become glued to the 



290 PART III. — PHYSIOLOGY. 

surface, affording them a secure hold upon it. The tendrils and 
their branches then coil into spirals, and acquire great firmness 
and elasticity, in the same manner as those of the Passion-flower 
above described. The plant is thus enabled to climb over perpen- 
dicular walls of rock, the sides of buildings, etc., objects to which 
most tendril- and leaf-climbers are unable to cling. A portion of 
Ampelopsis Veitchii is shown in Fig. 17, Part I. 

Not less wonderful is the sensitiveness of young roots, by reason 
of which they are able, during their progress through the soil, to 
avoid obstacles or turn aside from their course to reach supplies 
of moisture. 

Experiment proves that plants, like animals, may have their 
sensitiveness impaired or destroyed by exposure to anaesthetics 
like ether, chloroform, etc. 

If the Sensitive-plant be placed in a bell-jar under which a 
little chloroform is permitted to evaporate, its leaves very soon 
cease to respond to the touch; if the exposure be long continued, 
it fails to recover sensitiveness, and dies; but if it be of short 
duration, it soon comes to itself and the possession of its normal 
powers. This affords another proof that irritability in the plant 
is essentially the same thing as irritability in the animal. 

That all the protoplasts constituting the living portion of the 
plant are connected by delicate threads of protoplasm passing 
from cell to cell through the cell-walls, has already been shown. 
It is reasonable to assume that these threads conduct irritant 
impulses and serve thereby as a nervous mechanism, rudimentary 
indeed, but sufficient for the purpose of plants, whose responses to 
stimuli are exceedingly slow, as compared with those of animals. 

Reproduction. All plants possess the power of giving rise to 
new individuals, and this may take place in either one of two 
general ways, (1) by some form of cell division, and (2) by the 
union of two cells, at first distinct. The former mode is called 
asexual, and the latter, sexual reproduction. In the asexual mode 
we may distinguish between vegetative reproduction, in which 
the parent plant throws off or separates from itself ordinary vege- 
tative cells, and spore-reproduction, which consists of the separa- 
tion of specialized cells called asexual spores. The vegetative mode 
is represented in a very simple way by many of the low forms of 
plant life. The Red Snow-plant of the Arctic regions and the 
Bacteria multiply with astonishing rapidity by the simple process 



CHAPTER IV. — REPRODUCTION. 291 

of fission. Except that the cells become independent of each other, 
instead of remaining together to form colonies, the process 
resembles the cell-multiplication which takes place in the higher 
plants during growth. In the yeast and its allies, new individuals 
are formed by budding or by internal cell-formation. Most plants, 
even those belonging to the higher orders, have the power to 
multiply vegetatively. The Common Liverwort (Marchantia) , for 
example, produces on the surface of its fronds, little cup-like 
organs from which rounded masses of green cells are set free to 
give rise to new individuals; the Tiger Lily reproduces by means 
of bulblets formed in the leaf-axils; and many plants multiply, as 
we have seen, by bulbs, tubers, stolons, offsets, etc. 

Spore-reproduction by the asexual process is exemplified in 
many flowerless plants. The spores which are produced in such 
enormous numbers on the gills of the common Mushroom, many 
of the motile spores so commonly produced by the fresh-water 
Algae, and the ordinary spores of Equisetums, Club-Mosses and 
Ferns, are all products of this process. The spores are commonly 
borne in a special organ, called a sjjoranginm. 

There are also two principal modes of sexual reproduction. 
The simplest is by conjugation, which means the union of two 
similar gametes or sexual cells. 

The second mode is by fertilization, or the union of two sexual 
cells, or gametes, one of which is usually of larger size and 
passive, the egg cell; and the other, smaller and commonly active, 
the sperm cell. This mode is much the more common, and it exists 
in many varieties. It is the only sexual mode observed in all the 
higher types of plants. The description of its different modifica- 
tions is, however, reserved for Part IV, where they will be treated 
of in detail in our study of the principal types of plant life. 

There are few things in nature more wonderful than the results 
produced by fertilization. These, as w T e well know, are not con- 
fined to the immediate effects upon the fertilized cell itself, result- 
ing, in the case of flowerless plants, in the production of one or 
more spores, or in the case of flowering ones, in the development 
of an embryo, each capable of giving rise to a new plant; but the 
effects reach to adjacent organs, and often modify them in a pro- 
found manner. When Apple, Pumpkin or Melon blossoms are 
fertilized, not only do the ovules undergo great changes of struc- 
ture and size, but the entire ovary walls undergo a very remark- 
able development. In the Strawberry the influence extends to the 



292 PART III. — PHYSIOLOGY. 

receptacle, and in the Checkerberry to the calyx, in each case 
resulting in an extraordinary development of the organ. 

In the case of other organs the effect of fertilization may be 
of the opposite character, namely, to cause their rapid withering 
and decay, probably by a diversion of nutriment from them to 
other parts. This is nearly always the case with the corolla, and 
frequently also with the calyx, as every gardener knows, for if he 
wishes to prevent, as long as possible, his flowers from withering, 
he pinches off the anthers before they are ripe, or takes some other 
means to prevent fertilization. 

How far these effects are the result, more or less remote, of the 
stimulant effects of the fertilizing material on the egg-cell, and 
how far they are due to the stimulant effects of the pollen-tube 
on other tissues with which it comes in contact, is not yet known; 
but there are numerous facts to show that the effects cannot all 
be due to the fertilization of the ovule. 

The question naturally arises, why two modes of reproduction, 
the asexual and the sexual, should exist among plants. 

Comparing the two processes, we find that the asexual mode 
is simple, and involves little expenditure of energy on the part 
of the plant, while the other often requires for its consummation 
complicated machinery, and is an expensive process, a heavy draft 
on the vitality of the plant. Why, then, does the sexual mode 
exist? Science cannot yet give a complete answer to this ques- 
tion, but it may be partly answered by observing the difference 
between the offspring produced by the two processes. That of the 
asexual presents very little variation from the parental form. If 
we wish to perpetuate a fine variety of fruit, we do not sow the 
seeds, but rather multiply the plant by grafting, budding, layer- 
ing, or by some other process of division, imitating nature's modes 
of asexual multiplication. Should we plant the seeds, we would 
probably obtain a variety of fruits, those from different seeds 
differing more or less from each other and from the parent form, 
and all, very likely, inferior in excellence to the fruit we wish to 
perpetuate. Now, variation, which in this instance we wish to 
avoid, is of immense advantage to plants in their struggle for 
existence. The physical conditions of the earth's surface are slowly 
but constantly changing, and by variation, plants are constantly 
adapting themselves to these ever-changing conditions. Those 
varieties best adapted to the existing conditions are the ones to 
survive; those unfitted for them must perish. 



CHAPTER IV. — REPRODUCTION. 293 

The reason of the greater variation in sexually generated off- 
spring is to be sought for in the double parentage. The offspring 
of two individuals, or the product of two distinct lines of descent, 
must occasionally, at least, possess stronger characters — characters 
better adapted to insure the survival of the individual — than would 
be possible where the selection is made from one individual, or 
from one line of descent. Hence, the adoption and continuance 
of the more costly process of sexual reproduction is not an instance 
of extravagance on the part of nature, but is rather a wise economy 
of her forces — an investment which brings a profitable return. 
(See, also, Chapters XV and XVI of Part IV.) 



PART IV. 

TAXONOMY. 



CHAPTER I.— CLASSIFICATION AND NOMENCLATURE. 

Value of Comparative Study. Taxonomy is that department of 
botany which treats of classification, or the arrangement of plants 
in groups according to resemblances and differences. The study 
of plants in their relationships to each other, distinguishing be- 
tween differences which are superficial and those which are deep- 
lying, and noting how even the most diverse forms resemble each 
other fundamentally, is not only of engrossing interest, but one of 
the most necessary parts of botanical training. 

It is not possible, either, to understand any one plant thor- 
oughly, or even any one plant-organ, except by comparative study. 
We shall get, for example, a far more comprehensive view of the 
nature and functions of the leaf, if we compare the different 
modifications of it which occur on the Oak with those of the Pea, 
the Pitcher-plant, the Venus' Fly-trap, and the Clematis, than we 
should if we studied any one of them separately; so also we shall 
know more about the Rose plant if we study it in comparison with 
the Indian Corn, the Pine, the Fern and the Moss. 

Moreover, it is a matter of great interest and importance to 
the student to obtain a clear conception of the vegetable kingdom 
as a whole, as a great system of life. Of course, it is not possible, 
even if it were desirable, within the limits of an ordinary life- 
time, to become acquainted with all of the two hundred thousand 
or more species of plants known to science; but to get some 
accurate knowledge of the principal types, and of their relations 
to each other, to become thoroughly acquainted with a few of the 
representative forms of each type, and to be well acquainted with 
the flora of one's own neighborhood, is both possible and of great 
importance to every intelligent man. 



CHAPTER I.— CLASSIFICATION AND NOMENCLATURE. 295 

Classification and Naming of Plants. All plants are more Of 
less nearly related to each other, not only in structure and func- 
tion, but without doubt also genetically or by descent. 

The forms that gladden the face of the earth to-day are the 
descendants of the luxuriant vegetation of the far-off Carbonifer- 
ous Age, whose remains, in the form of coal, supply the civilized 
man of the present with fuel to warm his dwelling and drive his 
machinery; the coal plants, in turn, were descended from the still 
more remote and simpler vegetation of the Silurian seas. 

We shall best understand what plant classification means, the 
relation of past to present forms, and of present forms to each 
other, by means of a symbol — by picturing to our minds the system 
of life as a great tree. This tree began its life in the very remote 
past, in some very simple form, probably a shapeless bit of living 
jelly. From this as a common trunk, as time rolled on, branches 
diverged, which have continued to develop and ramify, and spread 
wider and wider, until the present time. Some branches, however, 
that throve for a time, were overshadowed by others, and finally 
decayed and died; but there still remain innumerable twigs and 
small branches of the wide-spreading top ; all else is buried in the 
debris of the past, its outlines only being traceable in the fossil 
remains which have been preserved to us. On examining the living 
twigs that remain, we naturally find them distributed into groups 
and clusters of various sizes. The members of a cluster of twigs 
we may trace back to a common branch, those of adjacent clusters 
similarly converge to other branches, and these again converge to 
larger ones, and so on. It is the business of the systematic bot- 
anist to move about among these twigs and branches of the great 
tree of vegetable life, and discover their real relationship to each 
other, to trace back the branches as far as possible toward the 
common trunk. 

Thus botanical classification has for its object the discovery of 
such natural or jrfiylogenetic relationship. 

Looking about among the varied forms of vegetation, the 
botanist finds plants that closely resemble each other in form, 
structure and habits of growth, and which are distinguished from 
other forms by some constant structural difference. For instance, 
the Smooth Rose, wherever found, maintains its essential charac- 
teristics, and differs constantly in some particulars from the Dog 
Rose, the Carolina Rose, the Prairie Rose, etc. Such a form is 
typified by one of the twigs of our figurative tree, and we call it a 



296 PART IV. — TAXONOMY. 

species. Species often resemble each other, as do the different 
species of Roses just mentioned. Such a group of species we call 
a genus, and that to which the roses belong we name the genus 
Rosa. Just as the species naturally fall into genera, so these, in 
turn, form higher groups, called families. The genus Pyrus, for 
example, which contains the Apple, Pear and Quince, resembles 
the genus Rosa in certain important and constant particulars in 
which it differs from all other plants. The same is true of the 
genus Rubus, which contains the Raspberries and Blackberries, 
the genus Crataegus, which contains the Hawthorns, and so on. 
These genera, therefore, are placed together in the family Rosa- 
cea. Similarly, families which resemble each other form orders, 
orders are grouped into classes; classes into divisions, and these 
are the primary divisions of the plant kingdom. 

It must not be understood that groups of the same name are 
always equal either in the sense of being equally numerous in sub- 
divisions or individuals, or in the sense of being marked off with 
equal distinctness from other groups; on the contrary, they are 
often very unequal in both senses, as we should naturally expect 
if we bear in mind our figure of the tree. Some species for exam- 
ple, are rare, they contain but few individuals, and these may not 
fall into distinct sub-groups or varieties; while others are exceed- 
ingly numerous, and may be broken up into many varieties; some 
species, at least so far as existing forms are concerned, are 
sharply marked off from other species, while others shade so insen- 
sibly into other species, by reason of connecting forms, that it is 
often difficult to draw the line between them. So it is also with 
the larger groups. When genera are large, they are often con- 
veniently divided into sub-genera; large families are commonly 
divided into sub-families, and these, perhaps, again into tribes. 
Classes, also, are often divided into sub-classes. The terms race 
and variety are applied to sub-divisions of species. 

The relation of the principal groups may be represented in the 
descending scale as follows: 
Division, 
Class, 
Order, 

Family, 
Genus, 

Species, 

Variety. 



CHAPTER I. — CLASSIFICATION AND NOMENCLATURE. 297 

In the classification of plants in a natural system, no one 
character or set of characters can be relied upon to the exclusion 
of the rest. The whole structure and development of the plant 
should be taken into account, in assigning it to its place in the 
system. It must not be understood, however, that all characters 
are of equal value, for this is far from being the case. For exam- 
ple, the cycle number of the flower is of much more value in 
classification than the shape of the petals, and the structure of 
the pistil has more significance than the character of the stem, 
whether it be herbaceous or woody. Moreover, the same char- 
acters do not always have the same value in some groups that 
they have in others. The shapes of leaves, for instance, in some 
genera afford convenient and reliable means of distinguishing 
species, while in others, these organs are so inconsistent in form 
as to be nearly worthless for the purposes of classification. In 
general, however, it may be said that characters drawn from the 
reproductive organs are of more value than those drawn from 
the vegetative, and those derived from structure are of more 
importance than those derived from the habits of the plant. The 
Elm and the Nettle, for example, resemble each other in important 
structural features, and belong to the same natural order, but 
their habits are widely different, the one being a pernicious 
pasture-weed, the other, one of the most magnificent and valuable 
of our forest trees. 

In the naming of plants, the binomial plan of nomenclature, 
first brought prominently into use by Linnaeus, is now universally 
adopted. This consists in applying the name of the genus and 
following it with the name of the species. According to this plan, 
the generic name must never be duplicated or applied to more 
than one genus, but the same specific name may be used again 
and again, providing it is appropriate and is not applied to more 
than one species of the same genus. The names, with rare excep- 
tions, are either of Latin origin or latinized from other languages. 
Solanum tuberosum, for example, is the name of the Potato plant, 
and Gentiana crinita, of the Fringed Gentian. The usage, it will 
be seen, is analogous to that employed in naming persons, except 
that the order of the names is reversed, the generic name corre- 
sponding to the surname, and the specific to the christian or given 
name. The plan has also obviously the same advantages. 

As to the origin of botanical names, some have come down to 
us from remote antiquity. Of these Petroselinum and Mandragora 



298 PART IV. TAXONOMY. 

are examples. The larger proportion, however, are of modern 
invention. Some of these were applied because of some useful 
property, real or fancied, which the plant was regarded as pos- 
sessing; for example, Scrophularia, because the plant was believed 
to be useful in scrofula; and Serpentaria, because the plant was 
thought to be a remedy for the bites of poisonous serpents. Some- 
times they were given in allusion to something in the appearance, 
habit, structure or behavior of the plant. Podophyllum, for exam- 
ple, has reference to the shape of the leaf; Dendrobium, to the 
epiphytic habit of the plant; Utricularia, to the fact that most of 
the species have small bladders on the leaves; and Impatiens, to 
the fact that the ripe capsules rupture explosively when touched. 

Very commonly, also, names were applied in honor of some 
naturalist, either the botanist who discovered or first accurately 
investigated and described the plant, or some other naturalist of 
eminence; for example, Linnsea was named in honor of the great 
Swedish naturalist, and Claytonia in honor of Clayton, an early 
American botanist. 

The first or generic name of the plant is always a noun, and 
should begin with a capital letter; the second, or specific name, 
may be either a qualifying adjective or a noun; it is much more 
commonly the former, and then should begin with a small letter, 
as in Bartonia verna and Lithospermum canescens. 

When the specific name is a noun, it may either be a proper 
name in the genitive case (corresponding to our English "pos- 
sessive"), as Co.rex Asa-Grayi (Gray's Sedge), and Iris Hookeri 
(Hooker's Iris) ; or it may be a common noun in the genitive, as 
Polygonum dumetorum (the Polygonum of the thickets), and 
Salix desertorum (the Willow of the deserts). In the first case, 
it should begin with a capital; in the second, with a small 
letter; but names which have previously been used as the names 
of genera, and have been reduced to those of species, are capital- 
ized, whether they were originally proper names or not; the fol- 
lowing are examples: Arissema Dracontium, Inula Helenium and 
Aristolochia Serpentaria. In zoology, the principle of beginning 
all specific names with a small letter is generally accepted; many 
botanists are adopting the same practice. 

In cases where species are sub-divided into varieties, the latter 
are designated by an additional name, as in the following exam- 
ples: Glycyrrhiza glabra typica, Prunus Amygdalus dulcis and 
Chenopodium ambrosioides anthelminticnm. 



CHAPTER I. — THE PRINCIPLE GROUPS OF PLANTS. 299 

A recognized rule among botanists is that the name which 
should finally attach to a plant is that which was first published. 
The publication, however, to be authoritative, must be accom- 
panied by an accurate description of the plant. By general con- 
sent, botanists have accepted the first edition of Linnaeus' "Species 
Plantarum," published in 1753, as the starting point for the publi- 
cation of both generic and specific names. Of course, it has very 
often happened in the history of the science, that several different 
botanists have investigated and named the same plant, and the 
question which name should be adopted is sometimes a difficult 
one to determine; some authors will perhaps adopt one name, and 
others another. To save confusion, in descriptive works it is 
customary to indicate, usually in abbreviation, the authority for 
the name. For example, Digitalis purpurea, L., Grindelia cunei- 
folia, Nutt., and Rhamnus Purshiana, D. C, the abbreviations 
standing for Linnaeus, Nuttall and De Candolle, respectively. When 
a species is transferred from the genus under which it was first 
published, the original specific name is retained with its authority; 
thus our Evergreen Wood-fern was named, by Linnaeus, Polypo- 
dium marginalis. The newer genus Dryopteris was later split off 
from the genus Polypodium. Asa Gray reclassified this plant 
under Dryopteris and we now have it named Dryopteris marginalis 
(L.) A. Gray. 

The names applied to groups of plants higher than genus, have 
the adjective form, and qualify the word Plants understood; for 
example, Angiospermx (meaning plantae angiospermae, or angio- 
permous plants), is applied to one of the main divisions of flower- 
ing-plants, and Rosace se (meaning plantae rosaceae, or rosaceous 
plants), is applied to the family which includes the Roses, Bram- 
bles, and Cinquefoils. Such names begin with a capital. 

Names applied to families are commonly made to terminate in 
ace&e, as for example, the names, Rosaceas, Vale'rianaceae, Rubia- 
cese, Caryophyllacese and Cucurbitacese; but the names Composite, 
Labiatse and Leguminosae are exceptions. Order names usually 
end in ales. 

Principal Groups of Plants. We shall treat of the plant king- 
dom under four great Divisions. These are the 

Thallophyta, Bryophyta, Pteridophyta, and Spermatophyta. 

It cannot be claimed that this is a strictly natural classifica- 
tion; probably in the present state of our knowledge it is not 
possible to make one which accurately represents the relations 



300 PART IV. TAXONOMY. 

of the lower forms of plant life. The future progress of the 
science will probably show that the Thallophytes include several 
groups at least as distinct from each other as the Pteridophytes 
are from the Spermatophytes. But this confessedly imperfect 
classification may still serve as a scaffolding with which to build 
the more perfect structure. 

It is beyond the scope of this work to give more than a general 
view of some of the principal types of plants under each Division. 



CHAPTEK II. 



DIVISION I.— THALLOPHYTA. 

CHARACTERISTICS. THE MYXOMYCETES. 

The name Thallophyta literally means "thallus-plants," and it 
alludes to the fact that in this group there is no clear differentia- 
tion of the plant-body into root, stem and leaf. It includes a vast 
number of forms differing widely from each other in structure, 
appearance and habit, some unicellular and the very simplest 
and smallest of organisms known, others comparatively com- 
plex and of large size. Not even the highest, however, ever 
possess true roots, though some are provided with root-like organs, 
called rhizoids, which serve mainly for anchorage or as holdfasts. 
A few of the higher forms show some differentiation of stem and 
leaf, but in no case is this distinction as sharp and clear as we 
find it in most plants belonging to the higher groups, and in the 
great majority of cases it is entirely wanting. While, also, the 
internal structure in some of the highest forms attains a consid- 
erable complexity, there is never a clear differentiation into epider- 
mal, fundamental and fibro-vascular systems of tissue, such as we 
find in Ferns and Flowering-plants. 

Between the highest and lowest forms of the Thallophytes there 
are various gradations of structure, and these are not always 
along the same line of development. Among unicellular forms 
every gradation may be seen between the simplest possible cells 
and those of the highest degree of complexity, and among multi- 
cellular forms, there are those in which the cells are united in the 



CHAPTER II. — THE THALLOPHYTA. — CHARACTERISTICS. 301 

simplest possible way, namely, in a linear series to form filaments, 
and the cells have so little dependence upon each other that they 
readily break apart to form distinct organisms.' There are those, 
again, in which the cells are somewhat more intimately united to 
form cell surfaces or flat expansions consisting of but one layer of 
cells; and there are still others which by cell-division in three 
planes, form masses. Among these, also, many gradations may be 
observed; some are cell-masses in which the component cells are 
nearly alike, and there is little difference between different parts of 
the organism; and there are others in which the component cells 
become developed into tissue-like groups, each differing from the 
other, but all closely inter-dependent, and where the plant grows 
into a definite form with a tendency to the development of distinct 
organs. 

In many members of this group, the multicellular forms are, 
as in the higher plants, the product of the division of a single cell ; 
in others, however, the mature plant-body is an aggregate of cells 
which were originally distinct but have come together to form a 
community. 

The great majority of the Thallophytes are at some period in 
their development endowed with the power of locomotion. Among 
the lowest forms the possession of this power may last during a 
considerable part of the life of the plant, while in the higher forms 
it is confined to the spore-period, or in some is wanting altogether. 

Their habits of life are also various; some are aquatic, others 
terrestrial; some are chlorophyll-bearing, flourishing only in the 
light and assimilating mineral matters, while others are chloro- 
phylless, indifferent to light, living as saprophytes or as parasites. 

They exhibit great variety also in their modes of reproduction. 
Among some of the lowest forms no mode is known except that 
of cell-division; in some others sexual reproduction takes place 
in its simplest form, by the union or conjugation of two similar 
sexual cells or gametes; in still others it takes place by the sim- 
plest mode of fertilization, which consists in the production of 
oospores in oogonia, and, lastly, in the highest forms it takes place 
by that mode of fertilization which results in the production of a 
fruiting organ, often quite complex in its character, called a 
sporocarp. 

About 80,000 species of Thallophytes are known, of which the 
Algae number about 14,000 and the Fungi about 66,000. 



302 part iv. taxonomy. 

The Myxomycetes, or Slime-Molds. 

i 

These are anomalous plants, so near the border-line between 
the animal and vegetable kingdoms, that some have regarded them 
as belonging to the one, and some to the other. They show little 
evidence of relationship to any other plants. The name is derived 
from myxos, slime, and mycetes, mold. They are, not uncommon, 
forming slimy masses amid decaying organic matters, especially 
decaying wood or leaves, or on forest soil. By far the great 
majority are saprophytes, while a few, as the curious one that 
causes the disease called "Club-root" on the Cabbage plant, are 
parasitic. (Fig. 505.) 

During their vegetable life, the typical slime molds consist of 
a naked, streaming mass of protoplasm known as a Plasmodium. 
This is net-like in structure, containing many nuclei but no chlo- 
rophyll. These plasmodia may range in size from a diameter of 
half an inch to an area of several square feet. They are usually 
white or yellow in color. They avoid the light, and creep about, 
amceba-like, among the organic debris on which they feed. 

Like the amceba, also, the slime molds surround and engulf 
particles of food instead of absorbing it in solution as other plants 
do. At the time of fructification, they creep to the surface and the 
whole Plasmodium takes part in the formation of one or more 
fructifying masses which may be net-like, irregular and sessile, 
resembling the plasmodia (plasmodiocarps) , or flat and cake-like 
with rudimentary walls (aethallia), or stalked (sporangia). Each 
of these, however, produce spores. When the fructification is ripe, 
it bursts, and very numerous thick-coated spores are discharged, 
commonly leaving behind a kind of frame-work which, being 
usually composed of capillary threads, is called a capillitium. 
When these asexual spores germinate, the naked protoplasts 
(swarm spores) escape and move about, sometimes at first by 
means of cilia, and then, losing their cilia, by amoeboid move- 
ments; more commonly, however, the movements are amceba-like 
from the very start. The moving particles, after growing consid- 
erably, divide, the movements in the meantime continuing. After 
a while, however, two or more of them come together, and the mass 
thus formed attracts other of the particles, which move toward it 
and unite with it, forming a colony of considerable size. The 
colony then sooner or later begins to develop its fructification. 



CHAPTER II. — THE MYXOMYCETES. OR SLIME MOLDS. 



303 



But before the fructifying period arrives, if the weather becomes 
dry and the conditions are not suitable for vegetative growth, the 
plants become motionless, shrink into compact and more or less 
rounded forms termed sclerotia, secrete a tough enclosing men\- 







%§&* 

•'•*#• 



p 






if 



i t 



Fig. 505. — Club-root of Cabbage, Plasmodiophora brassicae. 1, Turnip with 
club-root; 2, section of cabbage root with parenchyma cells filled with slime 
mold; 3, isolated parenchyma cell, (v) vacuole, (t) oil-drops in Plasmodium, 
(p) Plasmodium; 4, lower cell with Plasmodium, upper cell with spores develop- 
ing; 5, parenchyma cell with ripe spores; 6, isolated ripe spores; 7, germinating 
spores; 8, myxamoeba. (Harshberger.) 



304 



PART IV.— TAXONOMY. 



brane, and are then able to stand desiccation. When favorable 
conditions for growth return, the protoplasts escape from their 
enclosure and resume their activity. Some of the different stages 
in the development of these plants are represented in Fig. 506. 




Fig. 506. — Myxomycetes. 1. A group of sporangia of Stemonitis fusca. 
2, A single sporangium (x6). 3, Dendritic mass of sporangia of Spumaria alba 
on a Grass leaf. 4, Sporangium of Dictydium cernuum (x25). 5, A group of 
sporangia of the same. 6, and 7, Sporangia of Croterium minutum (6, x25). 
8. Sporangia of Arcyria punicea. 9, A single sporangium (xlO). 10, Part of 
the net-like capillitium of the same (xl60). 11. Fructification of Lycogala epi- 
dendrum on a piece of wood. 12, Leocarpus frap-ilis ; a Plasmodium on the 
right; several sporangia on the left. (Kerner and Oliver.) 



CHAPTER III. — THE SCHIZOMYCETES, OR BACTERIA. 305 

CHAPTER III.— THE THALLOPHYTA (Continued). 



THE SCHIZOMYCETES. — THE CYANOPHYCE^E. — THE 
FLAGELLATA.— THE DINOFLAGELLATA. 



THE SCHIZOMYCETES, OR BACTERIA. 

The term Schizomycetes is compounded of two Greek words, 
meaning literally "fission-fungi," in allusion to the way these 
plantg increase, by fission, and to their fungus-like habits. They 
are commonly known as Bacteria, and are at once the most abun- 
dant and the most minute of organisms. They range in size from 
0.1 micron (1/250,000 of an inch) in diameter up to 20 microns 
(1/1250 of an inch) in length. It requires for their study, there- 
fore, the highest and best powers of the microscope. They are all 
chlorophylless organisms, with nearly transparent cell-contents. 
They are found nearly everywhere, in water, in soil and on plants 
and animals. In all putrefying fluids, or solutions that contain 
decaying organic matters, they swarm in myriads. They are, in 
fact, the inciting cause of putrefaction. Some species of bacteria 
are harmless or even beneficial to man, while others are the source 
of some of the most dreaded and most fatal of diseases. A peculiar 
interest, therefore, attaches to the study of these organisms. 

The bacteria agree in having somewhat slimy as well as trans- 
parent walls and colorless cell-contents, which are not clearly 
differentiated into nucleus and cytoplasm. Different species differ 
considerably in form, size and in conditions and habits of growth. 
Their usual mode of increase is by fission. In some species the 
cells, after fission, immediately become independent; in others they 
remain united for a time to form filaments or chains of various 
lengths. The rapidity of this cell-division is so great that of some 
species one individual may produce millions of offspring in twenty- 
four hours. 

Many of the species, in some stage of their development, have 
the habit of secreting a jelly and increasing rapidly by fission, 
forming large gelatinous colonies. These are called zooglcea 
masses. They may be observed as a pellicle on bouillon, or on 
water in which organic substances are decaying. 

Many bacteria are motile, moving about freely, their locomotion 
being quite different from the Brownian movement. Their motion 
is usually due to the presence of flagella or cilia located usually at 



306 PART IV. — TAXONOMY. 

the ends of the cells either as a single flagellum or a tuft of them. 
Other species, perhaps as numerous, possess no flagella and are 
non-motile. * 

Under certain unfavorable conditions of temperature, food 
supply or moisture, some bacteria may pass into a resistant stage 
in which the protoplasm of the cell shrinks and is enclosed by a 
heavy inner wall, giving rise to a peculiar spore. These spores 
are very resistant to heat, cold and dryness, as well as to the 
action of antiseptics such as would quickly kill the fully-developed 
bacteria. 

Since bacteria live either in or upon their food supply, they 
have only to change it into soluble form in order to use it. Hence 
they secrete enzymes, by means of which they are able to assim- 
ilate their food, though commonly, as a result of enzyme action, 
by-products are presently formed which check the multiplication 
of the bacteria themselves. 

There is no group of plants in which it is at present so difficult 
to define the limits of species. It is difficult to classify them by 
their forms, because these, under certain conditions, have been 
found to change into others quite different, and a similar objection 
applies to classifying them according to their physiological effects, 
since it has been found that, in some instances at least, an innocent 
species may, in a different environment, be changed to one of great 
virulence and, vice versa, a virulent one may be changed to one 
that is harmless. 

Species which closely resemble each other in size and shape 
may show wide differences in their zooglcea or colony development 
and in their manner of living. The majority need oxygen for their 
growth and are termed aerobic, but some grow best away from 
oxygen and are termed anaerobic. Optional or facultative anae- 
robes can adapt themselves to either mode of existence. 

According to their form, three principal groups of bacteria 
are distinguished: the coccus or spherical forms, the bacillus or 
rod-like forms, and the spirillum or spirally bent forms. 

In the Coccus group the cells are globular and very small, 
appearing as minute dots under the microscope. In this group are 
included the micrococcus, in single, spherical forms exceedingly 
small; the streptococcus, in loosely united bead-like chains; the 
diplococcus, in pairs ; the staphylococcus, in grape-like clusters, and 
the sarcina, in cubical clusters. Related to these are the piano- 



CHAPTER III. — THE SCBIZOMYCETES. OK BACTERIA. 



10' 



sarcina and planococcus, which differ from the preceding groups 
in being motile. 

Among the rod-shaped organisms, the bacilli possess flagella or 
whip-like cilia and develop endospores, which the bacteria proper 
do not. The spirilla are motile by flagella at the extremities (polar 
flagella), but the cells are rigid, while in the spirochseta the spiral 
cells themselves are flexible. 

In the genus Beggiatoa the filaments are thicker and long; in 
the genus Cladothrix the filaments are branching; and in the genus 
Crenothrix they are simple but enclosed in a rather thick gelati- 
nous sheath. Some idea of the forms of bacteria may be gained 
from Fig. 507. 




Fif. 507. — Forms of Bacteria, a. Micrococcus, magnified about 1,800 diam- 
eters; b. Bacterium termo, magnified about 1.500 diameters; c, Bacillus tuber- 
culosis, magnified about 1,800 diameters ; d, Leptothrix buccalis, magnified about 
800 diameters; e, Beggiatoa alba, magnified about 600 diameters; f, Cladothrix 
dichotoma, magnified about 1,000 diameters; g, Crenothrix Kuehniana, magnified 
about 500 diameters; h, Spirillum undula, magnified about 800 diameters; i, 
Spirochaete plicatilis, magnified about 600 diameters. 



A classification according to some striking property or product 
of the organism, while not indicating relationship, is of practical 
value. For example, we may group bacteria as pathogenic or 
disease-producing, chromogenic or color-producing, zymogenic or 
ferment-producing, photogenic or light-producing, thermogenic or 
heat-producing, and saprogenic or decay-producing. 

Thus the phosphorescence observed on decaying sea fishes is 
due to photogenic bacteria ; the heating of silage, hay, manure and 
cotton waste, even giving rise to spontaneous combustion, is due 
to thermogenic organisms, while characteristically colored colonies 
are formed on culture media by many chromogenic forms, ranging 



308 PART IV. — TAXONOMY. 

through practically all the colors of the spectrum. Decay-produc- 
ing bacteria are responsible for the spoiling of poorly preserved 
foodstuffs and the development in these of the poisonous animal 
alkaloids known as ptomains. Fermentation bacteria are con- 
cerned in the souring of milk, the conversion of cider into vinegar, 
the ripening of cheese, the curing of tobacco and other important 
economic operations. Pathogenic bacteria are the inciting cause of 
a number of infectious diseases, such as typhoid fever, tuberculo- 
sis, diphtheria, cholera and leprosy. In their invasion of the 
human body, very poisonous substances known as toxins are gen- 
erated, these may be neutralized by the antitoxins formed by the 
body and resistance to the disease thus secured. Researches along 
these lines have resulted in the discovery of various methods for 
combatting or securing immunity from bacterial diseases and have 
aided in building up the important special science termed Bacteri- 
ology, to the text books of which the student is referred for further 
information on this very important subject. 

THE CYANOPHYCE^E, OR BLUE-GREEN ALG^E. 

The term is derived from two Greek words, which literally 
mean "blue-green sea-weed." They contain, in addition to chloro- 
phyll, a blue pigment, phycocyanin, and also, sometimes, reddish 
coloring matters in their cells. In some species the cells are dis- 
tinct; in others they are more or less united into chains or fila- 
ments. 

These plants are distributed widely, forming a bluish-green 
scum on or near the surface of stagnant water, either fresh or 
salt, and a slimy bluish-gray coating on wet soil, stones or logs. 
They are among the simplest plants capable of photo-synthesis 
and therefore of leading an independent existence. They flourish 
where there is organic matter, hence prefer sluggish streams and 
ponds. Some species can withstand high temperatures and thrive 
in hot springs; others are endophytic in habit, living within the 
cavities of larger and more highly organized plants. Some become 
united with Fungi to form Lichens. 

The Cyanophyceas are of slight economic interest, though at 
times they become so abundant as to give an offensive odor to 
drinking water. While in a few of the higher forms of Cyanophycese 
the protoplast is fairly well organized, in the lower forms there 
is little or no differentiation into nucleus and cytoplasm and the 



CHAPTER III. — THE CYANOPHYCE^E, OK BLUE-GREEN ALG^E. 309 

chlorophyll as well as the phycocyanin is diffused throughout the 
protoplast. Reproduction is entirely by vegetative methods, chiefly 
cell-division. 

The plant body is either an isolated cell, or, more commonly, a 
group or colony joined to form a filament or a plate. Gloeocapsa 
may be taken as an illustration. Like many of its congeners, it is 




Fig. 508. — Gloeocapsa. a, 
fully developed cell with 
gelatinous, greatly thick- 
ened and stratified cell- 
wall ; b, c, d, e, illustrate 
mode of multiplication, 
magnified about 150 diam- 
eters. 




Fig. 509. — Filament of 
Nostoc magnified about 
800 diameters, a, a heter- 

ocyst. 



found growing on damp rocks adjacent to springs, where they 
form slimy masses. The cell-walls swell and become converted 
into a stratified jelly, and in the meantime the cells .multiply by 
fission in different planes within the jelly, forming masses of vari- 
ous sizes. The plant and the way it multiplies are illustrated in 
Fig. 508. Other forms produce by division in one plane symmet- 
rical, tabular colonies, consisting of four, eight, sixteen, thirty-two 
or sixty-four rounded cells, held together by a firm gelatinous 
matrix. 

The Nostocs occur as greenish or brownish, tough gelatinous 
masses, some species of which are as large as walnuts, or even 
larger. They are common in ponds or slow streams, or on the 
damp ground bordering rivers, swamps and lakes. If a section 
be made of one of these masses and examined microscopically, it 
will be seen to contain, imbedded in the jelly, very numerous 
serpentine threads, composed of spherical cells loosely attached 
to each other in chains or moniliform rows. At intervals in the 
chain of cells occur larger and nearly colorless cells, called hetero- 
cysts. Fig. 509 shows one of these threads highly magnified. 



310 



PART IV. — TAXONOMY. 



Nostoc is also able to form resting cells, which are larger 
than the ordinary cells of the plant and are filled with food. Such 
cells can survive unfavorable conditions, such as cold and drought, 
and reproduce the plant filaments when conditions again become 
favorable. 




Fig. 510. — Portion of filament of Oscillatoria. magnified about 1.000 
diameters. 

The Oscillatorias are blue-green or brownish-green filamentous 
organisms, found abundantly in filthy ditches and ponds. The 
filaments are slender, usually somewhat coiled, and composed of 
compactly arranged short cylindrical cells, joined together end to 
end and provided with a gelatinous covering. The filaments are 
commonly agglomerated in masses, and each possesses a peculiar 
writhing or oscillating motion. It is to this that the name, Oscilla- 
toria, is due. Frequently the filaments break up transversely into 
short segments known as hormogones, each of which, escaping 
from its jelly-like covering, develops new filaments. Fig. 510 rep- 
resents a portion of one of the filaments. 







Fig. 511. — Portion of filament of Scytonema Naegellii, magnified 250 diam- 



The Scytonemas are also filamentous greenish or brownish 
plants, but they branch in a peculiar manner, as shown in the 
illustration, Fig. 511. Moreover, there are often more than one 
row of cells side by side, particularly in older filaments, and the 
cells are enclosed in a thick gelatinous envelope. Besides increas- 
ing by ordinary cell-division, they produce heterocysts and hormo- 
gones. 



CHAPTER III. — THE FLAGELLATA. 



311 



The Rivularias occur as small roundish gelatinous masses of 
radiating, somewhat branching filaments, each tipped with a trans- 
parent whip-like extension. At the opposite or basal end of the 
filament is a large rounded cell, the heterocyst. The plants, or 



Fig. 512. — Filament of Rivularia dura, magnified about 500 diameters. 

rather colonies, either float in the water or are attached to water- 
weeds, submerged rocks, etc. Fig. 512 shows a filament of one of 
the species. 



THE FLAGZLLATA. 

These are typically unicellular free-swimming fresh-water 
organisms, microscopic in size and generally regarded as bordering 
on both the animal and plant kingdoms. They form gelatinous 
colonies which may be either free-floating or attached, and either 
globular or branched. They have several characters in common 
with the unicellular animals (Protozoans) ; they are endowed with 
active locomotion by means of flagella, whence their name; many 
change their forms like the animal Amoeba; they possess contrac- 
tile vacuoles and red pigment spots, and grade quite perfectly into 
a distinctly animal group, the ciliate Infusoria. On the other hand, 
they possess chlorophyll and form thick-walled resting spores, 
hence are classified with plants. A common flagellate is the 
Euglena, usually found when fresh-water Algae are examined 
under the microscope. Its body is long, slender and one-celled; it 
bears a long flagellum at one end ; it contains a nucleus, several 




Fig. 513. — Euglena viridis. a, a, motile forms, each provided with a long 
Jlagellum and an "eye-spot" ; b, one of the cells passing into the encysted stage ; 
q, encysted form ; d, encysted form discharging minute swarm-spores. 



312 PART IV. — TAXONOMY. 

elongated chloroplasts, a contractile vacuole and a red pigment 
spot or "eye spot." Apparently this eye spot is sensitive to light, 
toward which the organism usually swims. Reproduction is by 
longitudinal fission, but in the autumn a thick-walled resting spore 
is formed which survives the winter and in the spring produces 
one or more new plants. Although ordinarily making its own 
food by photosynthesis, yet it can also exist in organic solutions as 
a saprophyte. 

Another flagellate, the Uroglena, is of interest because it some- 
times collects in water pipes and in decaying imparts an unpleas- 
ant oily flavor to water supplies. 

THE DINOFLAGELLATA OR PERIDIN^. 

Allied to the Flagellata is this small group of unicellular, free- 
swimming organisms which are mostly found floating in the sea, 
and with the Diatoms, constitute an important part of the plank- 
ton. (See page 451.) Some are luminous when disturbed and help 
to form the phosphorescence so often noted at sea. They are uni- 
cellular and possess a nucleus, vacuoles and large, brownish-yellow 
chromatophores. Characteristic of the group is the possession of 
two long cilia or flagella springing from the ventral surface in a 
longitudinal furrow. On cilia is directed backward, the other is 
curved and lies in a transverse furrow. The cell-walls are typ- 
ically plates of cellulose, perforated and often beautifully sculp- 
tured. A few species are destitute of chlorophyll and either live 
as saprophytes or even surround and enclose their food in the 
manner of the Amoeba. Reproduction by cell-division and by 
swarm spores is the rule. In the highest types a simple form of 
sexual reproduction has been met with. 



CHAPTER IV.— THE THALLOPHYTA (Continued). 

THE DIATOMEJE.— THE HETEROCONT^E. 
THE CHLOROPHYCEJE. 



THE DIATOMEjE, OR DIATOMS. 



The Diatoms are peculiar in the great variety of their shapes 
and in the strikingly beautiful sculpturing of their walls. They 
are in all reality unicellular, though sometimes united in colonies, 



CHAPTER IV. — THE DIATOMACEjE, OR DIATOMS. 313 

and all are microscopic in size. They possess chlorophyll, but the 
green color is more or less obscured by the presence of a peculiar 
brown coloring matter. Many are endowed with the power of 
locomotion, the movement being a gliding one, but some are pedi- 
celled and attached. 

The great distinguishing feature of the group, however, is the 
peculiar structure of the enclosing membrane. This is a silicious 
box consisting of two pieces fitting one into the other, like the 
parts of a common band-box. The two valves, as the parts of the 
box are called, are usually alike, excepting that one is a trifle 
larger than the other, so as to fit over it, and both are beautifully 
and often very delicately and regularly sculptured. 

Not less interesting and strange is their mode of reproduction. 
This takes place by fission, and in many species also sexually by 
conjugation, but the processes are peculiar. When the process of 
fission begins, the valves separate slightly from each other, the 
protoplasm divides into two portions, and each secretes for itself a 
new valve to fit within the old one that lies adjacent to it, and the 
plants thus become independent. 

It is evident that, as successive divisions take place, there will 
be a gradual reduction in the size of the plants, since the rigid 
valves once formed are not capable of expansion; so the process 
only goes on for a certain number of generations, when it is 
interrupted by the formation of what is called an auxospore. This 
may be formed asexually, simply by rejuvenation or the escape 
of the protoplasm from the old valves, or it may be the result of 
the conjugation of the protoplasm of two plants and the discarding 
of the old valves. In either case the new valves which are secreted 
are of the same size as those with which the first generation 
started. 

Diatoms are exceedingly abundant plants, both in individuals 
and in species, being found in nearly all waters, both salt and 
fresh, that are reasonably free from putrid matters. They occur 
in the tropics, in springs where waters are so hot that few other 
forms of life are able to survive, and in the ice-cold waters of the 
polar seas. About 6,000 species are known. Some of the different 
forms are represented in Figs. 514 to 518, inclusive. 

The flinty coverings or valves of the diatoms remain after their 
living substance is decayed. They even withstand incineration or 
the attack of strong acids. So-called "diatomaceous earth" is the 



314 



PART IV. — TAXONOMY. 



fossil remains of diatoms and is used as a base for many polishing 
powders as well as for a filtering medium. 




Fig. 515. 



Fig. 517 



Fig. 51! 



Fig. 514. — Side view of valves of Pinnularia dactylus, magnified about 300 
diameters. 

Fig. 515. — Front view of the same diatom, showing the way the valve6 fit 
together. 

Fig. 516. — Valve of Triceratium intermedium, magnified about 500 diam- 
eters. 

Fig. 517. — Triceratium favus, magnified about 150 diameters. 

Fig. 518. — Cosmiodiscus Normanianus. magnified about 600 diameters. 



THE HETEROCONT^E OR CONFERVA. 



This is a 3mall group of green algae, growing on wet soil or in 
water, and characterized by a peculiarity of their zoospores, which 
have cilia of unequal length. They are of little or no economic 
importance. The lower members of the group are related to the 
Flagellates, while the higher forms, such as Conferva, resemble the 
Chlorophyceae and were formerly included therewith. 

Conferva consists of slender, unbranched filaments and is 
widely distributed in fresh water. Its chloroplasts are yellowish- 
green and oil-forming. Reproduction is by the fragmentation of 
the filaments or by the production of zoospores. 



CHAPTER IV. — THE CHLOROPHYCE^E, OR GREEN ALG^E. 



315 



THE CHLOROPHVCE.E, OR GREEN ALGJE. 



This group includes quite a variety of forms, some simple in 
their structure, others comparatively complex. None of them 
possesses a soluble blue or brown coloring matter in the cells, 
though the spores of some, when ripe, have portions of the chloro- 
phyll modified into a substance chemically similar to the latter 
substances, but having a red color. Most 
..•■;•;>.. of the forms reproduce not only asex- 

:]-[v.\ •■>:.->. '•'';•.' ually by some mode of cell-division, but 

: £:'£*$i-: '•• V 'V' also sexually, either by conjugation or by 

"\V:'^V.'--- " the production of oogonia or antheridia 

resulting in the formation of oospores. 
They present wide diversity in size, 
shape and habit. Many beautiful forms 
occur in fresh water and, being easily 
collected, are favorite subjects of study. 
About nine thousand species are known, 
usually grouped in five orders: Sipho- 
nales, Protococcales, Volvocales, Confer- 
vales, Conjugales and Charales. 

Siphonales. These include both ma- 
rine and fresh-water forms. One of 
their most distinctive characteristics is 
the fact that, though often complex in 
form and attaining a considerable size, 
they are not divided into cells; each plant, 
in fact, may be regarded as a single 
highly elaborated cell. In a few species 
no sexual reproduction is known, in 
others it takes place by conjugating 
zoospores, and in still others, by fer- 
tilization and the production of oospores. 
Among the simplest forms of the 
group are the Botrydhims, one of which 
is represented in Fig. 519. The lower portion forms dichotomously 
branching root-like bodies or rhizoids, which penetrate the mud 
and serve for anchorage, while the balloon-shaped upper portion 
rises into the water above. This is filled with granular protoplasm 
and contains much chlorophyll. , 

The plants multiply in several different ways. When the ponds 




Fig. 519. — Botry aium gran- 
ulatum. in the act of dis- 
charging its zoospores. Mag- 
nified about 20 diameters. 
After Wolle. 



316 



FART IV. — TAXONOMY. 



in which they grow begin to dry up, the protoplasm descends into 
the rhizoids and there breaks up to form numerous rounded cells 
which are capable of enduring desiccation. When favorable con- 
ditions return, these either germinate and form new plants or 
immediately develop into sporangia. 

The upper or bulbous part of the plant, when mature, also 
becomes a sporangium. The spores discharged by this may be of 
two kinds; one kind, the zoospore, has but one cilium, and after 
moving about for a while it comes to rest and develops immediately 
into a new plant; the other kind, the gamete, possesses two cilia 
and fuses with another similar gamete (isogamete), forming a 
zygospore, and this, sooner or later, develops into a new plant. 
This figure shows the plant in the act of discharging its zoospores. 

a b 




Fig. 520. — Portions of fertile filaments of Vaucheria sessilis, showing mode of 
sexual reproduction, a, a, a, a, oogonia ; b, b, b, antheridia', c, 'oospore; d, e, 
germinating oospores; f, sperms. Magnified about 175 diameters. 



The Vaucherias, or Green Felts, occur as dense, felt-like masses 
in wet soil, on dripping rocks adjacent to springs, and in other 
similar situations. 

The individual filaments in some species attain a length of 
eight or ten inches. They root in the mud by means of rhizoids 
similar to those of Botrydium, and the filaments are more or less 
branching. Besides chlorophyll-bodies, they contain numerous oil- 
globules distributed through the interior of the tubes. They repro- 
duce asexually by rather large, multiciliate and multinucleate 
zoospores, formed by the separation of the ends of some of the 
branches. 



CHAPTER IV. — THE PROTOCOCCALES. 317 

Their mode of sexual reproduction is illustrated in Fig. 520. 
The oogonium, it will be seen, is an oval body borne laterally on 
the filament, and cut off from it by a partition. The antheridial 
branch, which is located adjacent to it, is slender and curved, a 
transverse partition is formed near its middle, and in the terminal 
cell thus produced are developed an immense number of very 
minute, ciliated sperms, which are discharged by a rupture of the 
cell-walls. Some of them find their way through the terminal 
opening of an oogonium, and fertilize the contained egg cell. It 
then develops into an oospore, which, after resting until the suc- 
ceeding spring, germinates. 

The species of Bryopsis, with beautiful feathery fronds; the 
Acetabularias, curious umbrella-shaped marine forms; and the 
Caulerpas, sea-shore plants, sometimes attaining a length of sev- 
eral yards, and having rhizoids, creeping stems and leaf-like 
branches, looking wonderfully like the much more highly organized 
multicellular plants, which have roots, stems and leaves, are also 
classed with the Siphonales. 

The Protococcales include a number of forms of unicellular, 
non-motile, green, water algse, some of which occur as isolated 
cells, while others consist of cells once distinct, which have grouped 
to form colonies. These colonies have a definite shape peculiar to 
the species, and are called ccenobia. Except on reproductive cells, 
cilia are lacking and the plants are not endowed with the power 
of locomotion, in this respect differing from the Volvocales. Cell- 
division occurs usually by internal cell-formation, and the cells 
always at first become distinct from each other, though they some- 
times unite afterwards, as we have seen, to form ccenobia. They 
reproduce asexually by means of zoospores, and most of them also 
sexually by the conjugation of zoospores of smaller size. 

Some forms live in the interior of other plants, though not 
parasitically. One of these, called Chlorochytrium Lemnse, grows 
in the intercellular spaces of the thallus of the common Duck-weed, 
Lemna trisulca. Others enter into the formation of Lichens. 

Pleurococcus or Protococcus is regarded as the simplest plant 
of this group. It consists of a single, spherical, non-motile cell, 
and forms thin, green coatings on damp earth or walls or on the 
trunks of trees. It has a definite wall, enclosing a lobed chloro- 
plast and a well-defined nucleus. It reproduces by cell-division 
only. (Fig. 521.) 

Scenedesmus, a common fresh-water Alga, forms simple colo- 



318 



PART IV. — TAXONOMY. 



nies with the cells, usually four in number, arranged in a row. Its 
reproduction is effected by the division, lengthwise, of each cell 
into four daughter cells which, on escaping from the parent cell, 
form a new colony. (Fig. 522.) 

Among the forms which produce more complex colonies are the 
Pediastrums and Hydrodictyon. The former are free microscopic 
forms, found abundantly in most fresh waters. The shapes of 





Fig. 521. 



Fig. 522. 



Fig. 521. — Pleurococcus vulgaris. Above, a single plant consisting of a 
single cell with a definite wall, well defined nucleus, and arge lobed chloro- 
past ; below, left, plants dividing; and below, right, a group of four separate 
plants, x 540. (After Strasburger from Martin.) 

Fig. 522. — A, Scenedesmus acutus. B. the same, undergoing division; C, 
Scenedesmus caudatus. (After Senn, x 1000. from Strasburger.) 

the colonies are roundish or stellately discoidal. Usually the 
central cells of the disc are polygonal, and those constituting the 
outer circle are commonly two-lobed. 

The contents of the cells after a time form small ciliated 
zoospores, which move about for a time on the interior of the cell. 
They then break through the membrane and escape; they soon 
come to rest, however, and divide again and again to form a colony, 
which at first consists of loosely and irregularly aggregated 
masses of cells. The colony now becomes enclosed in a mass of 
jelly secreted by its members, and then the latter arrange them- 
selves in one plane as already described. Instead of zoospores, 
gametes, similar in form but smaller and more numerous, may be 
formed. These being alike (isogametes) form zygospores and 
each zygospore upon germinating, develops into a new colony. 
Fig. 523 represents a plate-like colony of one of these plants. 

The Hydrodictyon, or Water-net, is an interesting fresh-water 
alga, not uncommon in ponds, lakes and slow streams. In the 
mature form of the plant the cells are arranged to form a quite 



CHAPTER IV. — THE VOLVOCALES. 



319 



regular net-work, which takes the shape of an elongated purse or 
bag, sometimes attaining a length of a yard or more. These float 
freely in quiet water with one end buoyed up by the bubbles of 
gas caught in it. Asexual reproduction takes place as follows: In 
the interior of some of the cells composing the mature net, the 
protoplasts break up and form a multitude of zoospores. These 
move about actively for a time within the parent cell and then 
arrange themselves to form minute new nets, which are finally set 
free by the rupture or solution of the enclosing walls, and in the 
course of a few weeks attain a size similar to that of the parent 
colony. 

In the sexual mode, numerous similar, but very much smaller 
ciliated gametes are formed in some of the special cells of the 
colony; these escape through the mother cell wall, pair and fuse, 
forming a zygospore. The latter produces zoospores which, after 
a resting stage, form new nets. 




Fig. 523.— Pedias- 
trium Boryanum, mag- 
nified 350 diameters. 





Fig. 524. — The Hydrodictyon or Water-net. a, portion of colony nearly 
natural size ; b, one of the cells of the colony greatly enlarged, showing in the 
interior minute cells arranging themselves to form a reticulum. 



Fig. 524, a, represents a portion of a mature Water-net not 
far from the natural size, and b, one of the cells greatly enlarged, 
showing numerous small cells in the interior, in the act of arrang- 
ing themselves into a net. 

The Volvocales consist of cells, either occurring singly or 
grouped in colonies, sometimes quite complex in structure. They 



320 



PART IV. — TAXONOMY. 



are provided in the vegetative, as well as in the spore stage, with 
cilia and have the power of locomotion, swimming about like 
animals. The plants are mostly fresh-water forms, and even the 
colonies are of small size, most of them microscopic. They multiply 
asexually by cell-division. The mode of sexual reproduction in 
some is by the conjugation of gametes, while in the higher forms 
of the group, the process is that of fertilization, the egg cell being 
of larger size and quiescent, while the sperm cell is small and 
provided with cilia. 

Among the unicellular forms Chlamydomonas may be taken to 
illustrate the simplest of the group. This plant is common in fresh 




Fig. 525. — Pandorina Morum, a fresh-water alga, a, colony of sixteen cells, 
each provided with a pair of cilia, by means of which the whole colony moves 
through the water with a rolling motion ; b, two zoospores of the same plant in 
the act of conjugation; c, the process nearly completed. Magnified about 150 
diameters. 



water and, being a free-swimming form, might readily be mistaken 
for a protozoan. The protoplast is somewhat globular, closely 
surrounded by a thin cell-wall, through which projects, at one end, 
two long cilia. The protoplast contains a large cup-shaped chloro- 
plast, a protein body, known as the pyrenoid, and usually sur- 
rounded by starch bodies, a nucleus, an "eye spot" of red pigment, 
and contractile vacuoles. Eeproduction is effected either by 
zoospores which are miniatures of the parent plant or by gametes 
which fuse in pairs to form resting zygospores which, later, ger- 
minate and become new plants. "Red snow" observed by travelers 
in arctic and alpine regions is produced by a species of Chlamy- 
domonas which secretes a bright red pigment and, when abundant 
and blown over the surface of the snow, gives rise to this appear- 
ance. 

Pandorina and Volvox may be taken to illustrate the forms 



CHAPTER IV. — THE VOLVOCALES. 321 

which produce colonies. In Pandorina the colony consists of six- 
teen, or less commonly of eight or thirty-two cells, crowded into a 
spheroidal mass, and surrounded by a transparent gelatinous 
envelope. Each cell possesses two cilia which project through the 
envelope and by which the colony is propelled with a rolling motion 
through the water. Asexual reproduction takes place by the 
formation of sixteen zoospore-like cells in the interior of any cell 
of the colony. These young cells remain together and after a time 
escape from the parent cell and form independent colonies. 

In the sexual reproduction, cell-division takes place as before, 
but the gametes which are formed escape from their enclosure by 
the softening of the gelatinous membrane and move about indi- 
vidually by means of their cilia, finally fusing and forming zygo- 
spores wiiich, when mature, acquire a brownish-red color. These 
after a period of rest germinate, produce gametes which pair and 
fuse, and then divide to form colonies of sixteen cells. See Fig. 525. 

Volvox globator is a more highly developed but similar plant 
also common in our fresh waters. When mature it has a diameter 
of about half that of an ordinary pin-head, and the cells composing 
it, which may number thousands, are so arranged as to form a 
hollow, spherical colony. The cells are chlorophyll-bearing and 
imbedded in a tough, gelatinous, transparent matrix; they are 
ordinarily connected with each other by threads of protoplasm, 
which form a delicate net-work over the surface, and each cell is 
provided with a pair of cilia which project beyond the enveloping 
membrane, and by their rhythmic vibrations communicate a rolling 
motion to the ccenobium. 

Asexual reproduction takes place as follows: At first the cells 
are all alike, but some enlarge and escape from the envelope into 
the interior of the sphere, where they form miniature colonies 
similar to the parent one. Often two or three of these colonies 
can be seen within the parent ccenobium. These continue to grow 
until the walls of the colony can no longer contain them, when by 
its rupturing, they escape and become independent. 

In the sexual reproduction, which occurs toward the close of the 
season, two distinct kinds of gametes are involved. Some of the 
cells enlarge, lose their cilia and develop into egg cells; these are 
the female gametes; other cells form numerous small, motile, male 
gametes or sperms. Both forms of gametes escape to the hollow 
of the spherical colony, where the sperms seek the eggs and fuse 



322 • PART IV. — TAXONOMY. 

with them. This is a prototype of fertilization such as occurs in 
the higher plants. 

After the resulting oospores have matured, the walls of the 
parent colony dissolve away and they are set free. Fig. 526 repre- 
sents a fertile colony of this species. 




ft' 

Fig. 526. — Volvox globator, magnifiedabout 75 diameters. a, one of the 
oogonia ; b, one of the antheridia fromwhich most of the sperms have escaped. 

The Confervales or Confervoid Algae. The plants of this group 
are the largest and most familiar of the Green Algae, chiefly 
inhabiting fresh waters. Most of them are either filamentous or 
they form a flattened thallus, consisting of a single layer, or at 
most of two layers, of cells. In a few forms the filaments are 
branching, in a few others, adjacent filaments anastomose, and 
in some, the component cells secrete a mucilage and become sep- 
arated from each other, forming a mucilaginous nia^s, in which the 
cells multiply by division. 

Most of the forms reproduce by asexual zoospores, many repro- 
duce sexually by means of zoospore-like gametes, which fuse 
together in pairs, forming a zygospore, and this upon germination, 
forms several zoospores which grow into new filaments ; still others 
produce oogonia containing oospheres, and antheridia which pro- 
duce ciliated sperms. 

The order includes a large number of forms, Ulva, Ulothrix, 
Cladophora, GEdogonium and Coleochaete. 

The Ulvas, so common in marine estuaries and salt marshes, 
are often called Sea-lettuce, from the shape of the bright-green 
fronds, which consist of thin, flattened or crispate membranous 



CHAPTER IV. — THK CONFERVALKS, OR CONFERVOID ALG.^E. 



323 



expansions, often several inches in breadth, and attached to 
stones, shells, etc. The fronds consist of two strata of cells, and 
increase in size by cell-division in two planes. In the early stages 
of their development, however, they are filamentous, but afterward, 
by cell-division in two planes, becomes laterally expanded. Fig. 527 
represents one of these plants. 




Fig. 527. — a. Ulva Lactuca. frond about natural size ; b, portion of frond 
magnified, showing arrangement of cells ; the unshaded ones are those from 
which zoospores have escaped; c. biciliated zoospores. 

The CEdogoniums are filamentous, mostly unbranching fresh- 
water alga?, whose cells are densely packed with chlorophyll-bodies. 
They are not uncommon in ponds, ditches and slow streams, where 
they occur in patches, attached by means of root-like processes to 
sticks, stones, the stems of aquatic plants, etc. There are a large 
number of species, some of them dioecious. They reproduce asex- 
ually, not only by the transverse fission of their cells, but by the 
production of zoospores. In the latter process, the protoplasm* of 
the cell becomes aggregated into a rounded or oblong mass, 
acquires a fringe of cilia at one end, escapes from the cell-wall, and 
moves through the water for a time, but finally comes to rest, sends 
out from one end root-like processes, attaches itself to some object 
in the water, and develops into a filament. See Fig. 528. 

In the sexual reproduction, one or more of the cells of the 
filament become greatly enlarged to form oogonia. When mature, 
an opening or pore is formed in each oogonium and sperm cells, 
produced either on another filament or in smaller cells of the same 
filament, find their way through these openings and fertilize the 
egg cells, of which there is but one in each oogonium. This is the 
common mode; in other species, however, small ciliated cells, called 



324 



PART IV. — TAXONOMY. 



androspores, are produced either in a male filament, or in other 
cells of the same filament that produces the oogonia; but these, 
instead of directly fertilizing the latter, become attached by a 
root-like process to it or near it, lose their cilia, grow into a short 
filament, and finally the terminal cell of the latter ruptures, setting 
free a minute sperm cell, which penetrates the aperture of the 
oogonium and fertilizes the egg cell, See Fig. 529, 




Fig. 529. 



Fig. 528.— CEdogonium, showing asexual modes of reproduction, a, portion 
of filament with the protoplasm escaping to become a free, ciliated cell, b ; c, the 
same cell throwing out rhizoids. Magnified about 250 diameters. 

Fig. 529. — CEdogonium ciliatum, showing mode of sexual reproduction. A, 
portion of male filament producing androspores b and c. B, portion of female 
filament producing oogonia e, e, e ; , f, male plants produced from androspores, 
which have germinated on the sides of two of the oogonia, and are each dis- 
charging a minute sperm. The filament has partially broken apart, leaving an 
opening in the top of the lower oogonium, so that the sperm cell may enter. 
This end of the oogonium is filled with mucilage, which slightly protrudes from 
the opening. C, a ripe oogonium, which has separated from the filament. D, 
represents the production of four ciliated spores from the germinating oospore. 



After fertilization, the oospore acquires a thick cell-wall, and 
in ripening changes to a brown color. The oogonium, with the 
ripened oospore still enclosed within its walls, now separates from 
the filament which bore it, and the spore, after a period of rest, 



CHAPTER IV. — THE CONFERVALES, OR CONFERVOID ALGJE. 325 

germinates. It does not, however, immediately develop into a 
filament, but first forms four ciliated zoospores. These, after 
moving about for a while, come to rest, and each develops into a 
filament. 




Fig. 530. — A, part of fertile thallus of Coleochaete pulvinata (magnified 350 
diameters). og, og, og, oogonia in various stages of development; an, an, 
antheridia ; z, z, sperms; s, s, zoospores; B, ripe oogonium in its cellular rind, r. 
After Pringsheim, from Sachs' Botany. 

Coleochsete. We may take Coleochsete pulvinata to illustrate 
this group. It occurs as small rounded, dark-green or olive-green 
masses, from 1/12 to 1/2 an inch in diameter, attached to stones, 
sticks or water-weeds in calcareous spring-waters. Each mass 
consists of a number of articulated, branching filaments, the cells 
composing which are oblong, narrower at the basal end, more or 
less dilated anteriorly, and often provided with a transparent hair 
or bristle, which has at its base a kind of sheath. 

The plants propagate themselves asexually by means of zoo- 
spores, which may arise from any of the vegetative cells, and 
sexually by means of oogonia and antheridia. The former are 
always modified terminal cells of a branch. The cell becomes 
swollen at the base and elongated into a tube at its apex, and 
when ready for fertilization, the tube opens and emits a colorless 
mucilage. The antheridia are small flask-shaped bodies, borne 
singly, or two or more together, at the ends of other branches, 
or on adjacent cells. Each of these when ripe emits a single sperm 



326 



PART IV. — TAXONOMY. 



cell. The latter moves about by means of two cilia, and probably 
finds its way through the mucilage down the tube of the oogonium 
to the egg cell at its base and fertilizes it. In the course of the 
ripening of the oogonium, there grows up about it from adjacent 
cells a cellular rind or protecting sheath. See Fig. 530, A and B. 
The ripe oospore does not immediately develop into the mature 
form of the plant, but, after a period of rest, first forms zoospores, 
from which the filaments are finally produced. 

The Conjugales or Conjugating Algae. This group differs from 
all other algae in the peculiarly complex structure of their chloro- 
phyll-bodies; from all, except some of the Diatomaceae, in their 




Fig. 531. — Spirogyra species; x 300. The cells of the filament on the left 
show successive stages in conjugation with the filament on the right, which has 
one cell in the vegetative condition, and one with a fully formed zygospore. 
(After L. Kny from G'anong.) 



mode of sexual reproduction, which consists in the direct conjuga- 
tion of ordinary vegetative cells to form zygospores, and from many 
in not producing zoospores nor swimming gametes. In some of the 
species the chlorophyll-bodies form plates of definite form and 
arrangement, in others, star-shaped masses, and in still others, 
spiral bands. A few of the forms are unicellular, but most of 
them consist of unbranching filaments. To this group belong a 
number of genera represented by species common in our fresh 



CHAPTER IV. — THE CONJUGALES, OR CONJUGATING ALGjE. 



327 



waters, most important of which are Mesocarpus, the Spirogyras, 
the Zygnemas and the Desmids. 

The Spirogyras are filamentous algae, very common in ponds 
and ditches, and they occur in masses of silky, green threads which 
sometimes attain a length of six or eight inches. The name Spiro- 
gyra was given in allusion to the fact that the chlorophyll-bodies 
form spiral bands winding around the cell adjacent to its interior 
wall. In some species the bands are single, in others there may be 
two or more. See Fig. 335, Part II. 

In conjugation, the cells of neighboring filaments grow toward 
one another in tubular projections which unite, forming a passage 
between the cells of the paired filaments. The protoplasts of one 
cell travel amceba-like into the other cell of the pair. After fusion, 
the zygospore thus formed secretes a thick wall and after a rest 
period is set free by the decay of the old filament, and upon 
germination forms a new filament. (Fig. 531.) 

The Zygnemas differ from the Spirogyras in having the chloro- 
phyll-bodies stellate in form and arranged axillary, a pair of them 
in each cell. (Fig. 336, Part II.) 

In Mesocarpus and some other related forms the zygospore is 
not formed within either of the conjugating cells but in the space 
between them, as shown in Fig. 532. 




Fig. 532. — Cells of two filaments of Mesocarpus scalaris with zygospore 
formed between them. Magnified about 350 diameters. 



The Desmids are found in great abundance and variety in clear, 
fresh water. They are mostly unicellular, but in some cases are 
loosely united into filaments. They have cellulose walls surrounded 
by a transparent gelatinous substance. They are usually more or 
less constricted in the middle, and in this isthmus-like constricted 
part the nucleus is situated. Each symmetrical half contains a 
chloroplast and a number of pyrenoids. They contain large green 



328 PART IV. TAXONOMY. 

chloroplasts, often compound and elaborate. The species are 
exceedingly numerous; many are lobed, spinose, delicately striated 
or otherwise ornamented. 

Asexual reproduction takes place by division along the plane 
of symmetry between the halves. The new wall thus formed is 
double, and on each side of it is formed a new semi-cell. When 
these reach a size about as great as that of the old semi-cells, 




Fig. 533. — Cosmarium Botrytis, a Desmid. showing process of division. a, 
the mature plant ; b, the plant in any early stage of division, with two new semi- 
cells forming between the old ones ; c, the process nearly completed. Magnified 
about 500 diameters. 

separation takes place. Each of the new plants thus formed, 
therefore, consists of an old and a newly-formed semi-cell. This 
mode of multiplication is illustrated in Fig. 533. 

Sexual reproduction takes place usually late in the season, and 
consists in the conjugation of two cells which come together, their 
protoplasts escaping through ruptures at the isthmus and fusing 
to form a zygospore. The zygospore differs considerably in appear- 
ance in different species. Sometimes it is smooth and spherical, at 
others warty or tuberculate, and in still others spiny, as in Fig. 
534, which illustrates the sexual reproduction of Cosmarium 
Botrytis. • 

In Fig. 535 are represented several other forms of Desmids. 

The Charales or Stoneworts. These are submerged fresh-water 
plants, rooting in the muddy bottoms of ditches, ponds and sluggish 
streams. They are able to deposit lime from solution and thus 
become encrusted with it, hence the popular name, Stoneworts. 



CHAPTER IV. — THE CHARALES, OR STONEWORTS. 



329 



They do not possess true roots, but fasten themselves to the mud 
by means of root-like processes called rhizoids. They bear at 
intervals on the slender stems whorled appendages, which may be 




Fig. 534. — Conjugation of Cosmarium Botrytis. a, zygospore ; b, b', b' 
b"', the empty semi-cells of the two plants. Magnified about 500 diameters. 




Fig. 535. — Desmids. a, Closterium Ehrenbergii, magnified 100 diameters; 
b, Xanthidium fasciculatum, magnified 500 diameters ; c, Micrasterias radiosa, 
magnified 200 diameters ; d, Euastrum elegans, magnified 500 diameters ; e, Cos- 
marium pardalis (?), magnified 500 diameters; f, Micrasterias pinnatifida, magni- 
fied about 400 diameters. 



330 



PART IV. — TAXONOMY. 



taken to represent leaves, and in 
the axils of these, branches occur. 
See Fig. 536. The stem increases 
in length by the continual divi- 
sion of the apical cell in a trans- 
verse direction, and by the growth 
in length of some of the cells thus 
produced. The cells resulting 
from this division are alternately 
nodal and internodal cells. The 
latter become multinucleated and 
greatly elongated, sometimes sev- 
eral inches in length, but do not 
again divide. Not so, however, 
with the nodal cells. These in- 
crease but little in length, but 
divide longitudinally to produce 
the lateral appendages, — leaves, 
stems and fruiting organs. From 
them also originates the cellular 
cortex which in the genus Chara, 
but not in the related genus 
Nitella, covers the internodal cell 
and keeps pace with its growth. 
In this mode of growth, as well 
as in the structure of their fruit- 
ing organs, the Stoneworts are 
peculiar among plants. In com- 
plexity of structure, also, they 
rank highest among Algae. The 
plants are abundant in species, 
and are widely distributed over 
the world, but they all belong to 
the two genera already men- 
tioned. Some are of small size, 
only one or two inches high; 
other species attain the height of 
two or three feet. Nearly all are 
gregarious in their habits. 

They agree with the Conjugates in not producing zoospores, 
their asexual reproduction being by means of tuber-like structures 




536. 



Portion of Chara plant, 
about natural size, showing arrange- 
ment of leaves and branches. 



CHAPTER IV. — THE CHARALES, OR STONEWORTS. 



331 



borne on the subterranean parts, or by peculiar branches which 
form rhizoids on their basal nodes and become separated from the 
parent plant. 

They reproduce sexually by means of oogonia and antheridia, 
both of which have interesting- peculiarities in their structure. 
These organs are, in some species, both borne on the same plant; 
in others, on different individuals; they occur at the nodes, often 
close together. The oogonium is at first a single cell, but in the 




Fig. 537. 



Fig. 538. 



Fig. 537. — Small portion of Chara stem, showing one node on which are 
borne an oogonium, a. arid an antheridium, b. c, is a leaf, most of the other 
leaves having been removed. Enlarged about ten diameters. 

Fig. 538. — Segment of Antheridium of Chara. a. one of the wall-cells; 
m, manubrium; f, f. antheridia] filaments. Magnified about 100 diameters. 



course of its development it divides transversely, and the apical 
cell becomes enlarged and develops into a germ-cell. This soon 
becomes covered by a layer of cells growing up from the base and 
coiled spirally around it, and these are surmounted by a crown, 
which in Chara consists of five and in Nitella of ten smaller cells, 
which originate from the others by transverse division. Thus, just 
before maturity, the large egg cell is completely enclosed, but when 
ready for fertilization, an opening occurs between the cells at the 
apex, and this becomes filled with mucilage, and the wall of the 
germ-cell is also converted into mucilage at its apex, permitting 
the entrance of the sperms. The oogonium, when mature, is 
oblong or ellipsoidal in form and of a deep orange color. See 
Fig. 537. 

The antheridium is a spherical body nearly as large as the 



332 



PART IV. — TAXONOMY. 



oogonium, and also orange-colored when ripe. Its walls are com- 
posesd of eight triangular cells, whose edges are serrated or wavy, 
and nicely dovetail into each other. To the centre of each one of 
these cells, and projecting interiorly, is attached a cylindrical cell, 
called the manubrium, and this bears at its inner apex a rounded 
cell called the head-cell. This, in turn, is surmounted by about six 
smaller cells, from which proceed a number of small, coiled fila- 
ments, each made up of about two hundred disc-shaped cells. In 
all, each antheridium contains from one hundred to two hundred 
of these filaments. See Fig. 538. When the antheridium is ripe 
the segments of the wall separate, and from each cell of the fila- 
ments there escapes a minute, slender, coiled sperm cell, provided 
at its smaller end with two long cilia, by means of which it moves 
actively through the water. Some of them find their way into the 
oogonia and fertilize them. See Fig. 539, After fertilization the 




Fig. 539. — Portion of one of the antheridial filaments, magnified about 800 
diameters, showing sperms in all of the cells but two ; from these the sperms 
have escaped, and are shown at a, a. 



outer cells of the oogonium harden, forming a protective coat for 
the oospore. 

The ripe spore rests for a time, and then, either in the autumn 
or early spring, germinates. It does not, however, immediately 
produce the leafy plant, but develops a filament of cells, called the 
pro-embryo. From this the leafy plant springs as a lateral shoot, 
and the pro-embryo afterwards perishes. 



CHATTER V.— THE PHiEOPHYCEiE, OR BROWN ALGJE. 333 

CHAPTER V.— THE THALLOPHYTA (Continued). 
THE PH^OPHYCEiE.— THE RHODOPHYCE>£. 



THE PH^EOPHYCE^, OR BROWN ALG^E. 

The Phaeophyceae are practically all marine plants, and are 
among the most abundant as well as the largest plants of the 
ocean. They reach their greatest size in the colder waters. While 
some are small, others attain gigantic dimensions, Macrocystis, for 
instance, having a length of stem which considerably exceeds that 
of the tallest Australian Eucalyptus trees and California conifers. 
In complexity of structure, also, the group presents great differ- 
ences, some being quite simple, others among the most complex of 
their class, but the simplest are connected with the most complex 
by almost innumerable gradations. 

They all possess, in addition to chlorophyll, a peculiar brown 
coloring matter, fucoxanthin, related to that found in the Diatoms, 
and hence they have an olive-green or brownish instead of a bright- 
green color. They are, on this account, called Brown Sea-weeds. 

There are two principal divisions of the Phseophycese, the Phxo- 
sporales, and the Fucales. 

The term Phsesporales literally means dusky-spored, and is 
applied to the group because of the unusually dark color of the 
sporangia. Many of the species have been observed to produce 
gemmae, or to multiply by the separation of branches; but spore- 
reproduction takes place by means of small, ciliated gametes, 
formed in special cells on the surface of the fronds; the zygospores 
resulting grow directly into new plants similar to the parents. 
Some species produce only round, dark-colored, unilocular sporan- 
gia; others produce these and also oblong multilocular sporangia. 

The most familiar members of the group are the Laminarias 
or Sea-aprons. These are plants of large size, some attaining a 
length of twenty to thirty feet. They have cylindrical stems of 
varying length, and often attaining the diameter of an inch or 
more. The base is attached firmly to rocks or other marine objects 
by means of strong, branching rhizoids, and the upper part 
expands into a flattened, leathery, blade-like organ, which in some 
species is entire; in others more or less divided. The blade and 
stem increase in length in a peculiar manner, namely, by the 



334 PART IV. — TAXONOMY. 

formation of new cells at the junction of the two organs, and the 
stem also increases in diameter by means of a growing layer 
beneath the rind, reminding us of the growth of the stems of Dico- 
tyledons. 

Fig. 540 represents a plant of Laminaria saccharina, about 
one-thirtieth natural size. To this group also belong the Nereo- 
cystis, with its very long stalk, single great float and broad blades, 
the Postelsia or Sea Palm, and the gigantic Macrocystis. 

The Fucales or Rockweeds are dark olive-green algse of consider- 
able size, and having a cartilaginous consistency. Most of them 
adhere firmly to rocks by means of branching discs, but a few float 
free in the ocean waters. The vegetative body consists either of 
a dichotomously branching, more or less flattened thallus, as in the 
genus Fucus, or of fairly differentiated stems and leaves, as in 
Sargassum, the Gulfweed of the Sargasso Sea. Many of the 
species possess air-bladders, which render the branches buoyant. 

They differ from the previous group in their more complex 
mode of sexual reproduction. This takes place by means of anther- 
idia and oogonia. 

We may take the common Bladder-wrack, Fucus vesiculosus, 
as the type of the group. A portion of the plant is shown in Fig. 
541. It grows attached by discoid holdfasts to rocks, between 
high and low tide. The frond is flattened, cartilaginous, two or 
three feet in length, and repeatedly forking. It has a prominent 
midrib, and on either side of it, at intervals, air-vesicles occur in 
pairs. The fruiting organs occur at the ends of certain branches, 
in cavities called conceptacles, which are arranged close together, 
and consist of globular depressions in the surface. The walls of 
the conceptacles are lined with hairs, some of - which protrude 
from the narrow opening. Among these hairs, on the "interior of 
some of the conceptacles, are borne antheridia, and in others 
oogonia; but in some species, for example, Fucus platy carpus, both 
are borne in the same conceptacle. A female conceptacle is shown 
in Fig. 542. 

The antheridia are branching filaments, some of the cells of 
which, when mature, emit numerous bi-ciliated sperm cells. These 
find their way to the egg cells, which, in the meantime, have 
escaped from the oogonia, and fertilize them. Fig. 503 shows one 
of the branching filaments bearing antheridia. 

The oogonium begins as a minute papilla-like protuberance on 
the wall of the conceptacle, and is at first a single cell. This 



'HAPTER V. — THE PH^EOPHYCE^E, OR BROWN ALG^E. 335 






?ri: 





Fig. 542. 



Fig. 540. 



Fig. 540. — Laminaria saccharina, about one-thirtieth 
natural size. 

> Fig. 541. — Portion of thallus of Fucus vesiculosus, 
about natural size; a, one of the bladders; b, fruiting 
organs. 

Fig. 542. — Female conceptacle of Fucus vesicu- 
losis, producing on its interior, hairs and oogonia. 
Magnified about 40 diameters. 



336 



PART IV.— TAXONOMY. 



divides transversely into two cells, the lower one constituting the 
stalk, and the other becoming the oogonium proper. This becomes 
relatively large in size and spheroidal in form, and, in this species, 
the protoplasmic contents break up into eight nearly equal por- 
tions, forming as many egg cells. In most other members of the 





Fig. 543. 

Fig. 543. — One of the branching filaments from a male conceptacle of Fucus 
vesiculosis bearing antheridia, a. Magnified about 150 diameters. 

Fig. 544.- — Escaped egg cell from one of the oogonia, with ciliated sperms 
swarming about it. Magnified about 400 diameters. 

order, either no division takes place, and but a single egg cell is 
formed within the oogonium, or else fewer are formed than in 
Fucus. 

When the egg cells are fully formed, the wall of the oogonium 
ruptures and they are discharged into the water, and there the 
sperm cells swarm about them and fertilize them. See Fig. 544. 
After this process is completed the oospore acquires a cell wall, 
and soon begins to germinate. 



THE RHODOPHYCE^E, OR RED ALG^E. 

This group includes the red or violet-colored algse, popularly 
known as "Sea-Mosses" or Eed Marine Algse. They are exceed- 
ingly numerous in species, and are widely distributed in ocean 
waters. A few also, as Batrachospermum and Bangia, inhabit 
fresh waters. The marine forms mostly grow attached to rocks 
or shells below the level of low tide, some at considerable depths, 
as far down as light can penetrate — about two hundred feet in 



CHAPTER V. — THE RHODOPHYCEjE, OR RED ALG^. 337 

clear waters. They are chlorophyll-plants, but the proper green 
color is more or less obscured by the presence of a red or violet 
coloring matter, phycoerythrin. Some have also a blue pigment, 
phycocyanin. In the simpler forms the thallus consists of branch- 
ing filaments; in others it forms a flat expansion, consisting of one 
or more strata of cells, sometimes with a midrib, giving the struc- 
ture an appearance something like that of a leaf; in other 
instances tissue-like structures, often possessing considerable com- 
plexity, originate from the growing together of adjacent branches; 
and in still others true tissues appear to be formed. Some species 
are quite gelatinous and have some food value, notably Chondrus 
Crispus and Gigartina mamillosa, which constitute Irish Moss, and 
several Asiatic species of Gracilaria, Gelidium and Gloiopeltis, 
from which Agar is extracted. In the majority of cases growth 
takes place by the division of a single apical cell, but in the Coral- 
lines and their relatives, there are usually several initial cells. 
This group is also distinguished from the rest by the fact that 
they secrete large quantities of lime in their cells. 

The most distinguishing characteristic of the group is their 
mode of reproduction. In their asexual reproduction they produce 
non-motile cells, called tetraspores, which, as the name indicates, 
are usually formed in fours in the mother-cell. This, however, is 
not always the case; sometimes there are but one or two, occa- 
sionally as many as eight. In the forms which consist of branch- 
ing filaments, the tetraspores are usually formed in the terminal 
cells of the branches; in other species they are usually imbedded 
in clusters in the tissues of certain branches, which consequently 
often acquire a form quite different from the rest. The plant 
which bears the tetraspores has no sex organs, but the tetraspores 
upon escaping, germinate and grow into plants that bear sex 
organs. Fig. 545 represents a small portion of the thallus of a 
species of Plocamium highly magnified, showing tetraspores. 

The sex organs consist of antheridia and procarps, the latter 
containing the carpogonia. These may both be borne on the same 
plant, or, as is more commonly the case, on separate plants of the 
same species. The antheridia occur either' singly or in groups at 
the ends of certain branches, and the sperm cells are minute, 
rounded, non-ciliated and non-motile particles, and are dependent 
therefore on water-currents or on animalcula for their conveyance 
to the procarp. The latter are more complex organs than the 
oogonia of other algae. In the course of their development, the 



33* 



PART IV. — TAXONOMY. 



unicellular or multicellular mass first formed becomes differen- 
tiated into two portions, an upper portion, called the trichogyne, 
usually a straight, hair-like process, and an enlarged basal por- 
tion, the carpogonium. 





Fig. 546. 



. 545. — Small portion of thallus 
species of Plocamium, one of the 



Fig. 545. 



F 
of c 

Red Algae, showing branches bea 
tetraspores, t. Magnified about 75 
diameters. 

Fig. 546. — Lejosisia mediterranea, 
one of the Red Marine Algae ; portion 
of filament, showing asexual reproduc- 
tion by tetraspores. a, represents tetra- 
sporangium. Three of the four spores 
are shown in the figure, the other is 
concealed behind them. 



The part which receives the fertilizing influence of the sperm 
cells is the trichogyne, but this does not undergo development in 
consequence, but communicates the influence to the carpogonium, 
and then soon withers away, while the latter undergoes very con- 
siderable changes. These differ considerably in different species, 
but in all, the fertilization stimulates a considerable vegetative 
growth, which results in the production of a cystocarp containing 
a number of asexual spores, called carpospores. 

Upon germination, the carpospores produce the sexual plants, 
thus completing the life cycle. We observe here for the first time 
the alternation of sexual and asexual generations which is so well 
established in the higher plants. 



CHAPTER VI. — CHARACTERISTICS OF THE FUNGI. 



339 



In some cases, as in Nemalion, fertilization results in the out- 
growth of several branches from the basal part, which break up 
into cells, each one of which becomes a carpospore. In other cases, 
as in Lejolisia, the stimulant influence results in the development 




Fig. 547. — Lejolisia mediterranea ; portion of fertile filament, showing mode 
of sexual reproduction. a, antheridium nearly ripe ; b, ripe antheridium with 
escaping sperm cells; c, carpogonium, bearing at its apex a trichogyne, to which 
two sperm cells are attached; d, cystocarp, showing carpospores in its interior; 
e, cystocarp discharging one of its carpospores, f. Magnified about 150 diam- 
eters. 

of adjacent cells to form filaments which grow up around the 
cystocarp, and unite laterally to form an envelope to enclose it. 
Both the sexual and asexual processes in this plant are illustrated 
in Figs. 546 and 547. 



CHAPTER VI.— THE THALLOPHYTA (Continued) 

THE FUNGI.— THE PHYCOMYCETES.— THE 
CHYTRIDIACE^.— THE ASCOMYCETES. 

CHARACTERISTICS OF THE FUNGI. 



The Fungi are generally regarded as degenerate descendents of 
the Algae, which, having lost their chlorophyll and therefore their 
power of independent living, have now become parasites or sapro- 



340 PART IV. — TAXONOMY. 

phytes. The distinction between these two groups is not sharply 
drawn. Thus some parasites are able to exist as saprophytes when 
occasion requires and are called facultative saprophytes, while 
others cannot adjust themselves to any other mode of existence 
and are obligate parasites. 

There are several thousand species of fungi. The vegetative 
body of the fungus consists of a mycelium made up of colorless, 
branched thread-like cells known as hyphae, which in saprophytes 
ramify among the decaying organic debris of the substratum or 
in parasites invade the living tissue of the plant or animal host 
and draw nourishment from them. In some instances there are 
formed club-shaped branches of the mycelia especially fitted to 
absorb food material. Such branches are termed haustoria. The 
mycelia of some species of parasitic fungi grow on the surface of 
the host and are epiphytic, while in other species they live within 
the tissues of the host and are endophytic. 

Some fungi live in symbiotic relations or partnerships with 
green plants, and this without apparent injury to the latter. Of 
such nature are the mycorhizas formed in connection with the 
roots of trees (see also page 276). Lichens, to be later described, 
are peculiar unions of alga and fungus in which the alga provides 
the carbonaceous food while the fungus holds fast the plant body 
to the substratum. 

In the simpler mycelial forms, the hyphae occur singly or more 
or less interwoven into a tangled felt-work, but they are not gath- 
ered into definite forms, and have little or no dependence upon 
each other; in the higher groups, however, there is more or less 
division of labor among the hyphae, and they become consolidated 
into false tissues, which acquire definite shapes according to the 
species. Of this character are the fructifying organs or carpo- 
spores, which constitute the above-ground parts of the Agarics, 
Puff-balls, Cup-fungi, etc., and the sclerotium, a compact, hard 
mass of thick-walled hyphae, which serves as a resting-stage in the 
development of some species, as the Ergot of Rye. 

In their reproduction, the fungi show resemblances to the green 
algae, presumably their ancestors. Asexual spores formed in great 
numbers are usually responsible for the rapid spread of fungous 
diseases. Of such nature are conidia, which are merely cells cut 
off from the ends of certain hyphae. Similar asexual spores are the 
uredospores of the rusts and the basidiospores of the mushrooms. 
Others, formed in spore cases or sporangia, or in special recep- 



CHAPTER VI. — THE PHYCOMYCETES, OK ALGAL FUNGI. -541 

tacles of various kinds, will be described in connection with the 
groups in which they are formed. In some fungi, sexual organs 
are formed by specially modified hyphae, and a variety of sexual 
spores, chief among which are zygospores, oospores and ascospores 
are thus produced. 

Classification of the fungi is difficult, for, owing to their degen- 
erate mode of life, the structures through which their relationship 
might be traced, have become greatly changed. The names of the 
principal groups end characteristically in "mycetes" (meaning 
fungus). Thus we have the Eumycetes or True Fungi, divided 
into the Phycomycetcs or Alga-like Fungi, the Ascomycetes, or 
Sac-Fungi, and the Basidiomycetes, or Basidia Fungi. The re- 
mainder of the fungi, including those whose life histories are 
incompletely known, are placed in the artificial .group of Fungi 
Imperfecta 

THE PHYCOMYCETES OR ALGAL FUNGI. 

The term Phycomycetes literally means "Sea-weed Fungi," 
and alludes to the resemblance, in the mode of sexual reproduc- 
tion, between these plants and certain of the Green Algae. They 
produce a copious mycelium, which usually consists of unsegmented 
hyphae, bear conidia, and most of them reproduce sexually either 
by zygospores or oospores. 

There are three orders, the Zygomycetales, the Peronosporales, 
and the Saprolegniales. 

Of the Zygomycetales, or Conjugating-Fungi, Mucor Mucedo 
may be taken as an example. This mold is a very common one 
found growing on various kinds of decaying matters, such as 
horse-dung, rotten fruits, etc. The mycelium, which is unicel- 
lular, extends its finer hyphae through the nutritive substratum, 
while its coarser hyphae form a cobweb-like growth on the surface 
of the latter. Both are profusely branched. 

The fruiting hyphae, however, are simple, and grow out into 
the air, each bearing at its tip a globular, blackish sporangium, 
the wall of which soon ruptures, setting free numerous conidia. 
This is the asexual mode of reproduction. Sexual reproduction 
takes place by conjugation of two similar or somewhat dissimilar 
gametes, which are merely cells cut off from the ends of the hyphae. 
These fuse and form large, rounded, thick-walled zygospores, 
which rest for a time before germinating, and then, if the supply 



34S 



PART IV. — TAXONOMY. 



of nourishment is sufficient, develop a copious vegetative mycelium ; 
if insufficiently nourished they produce at once aerial hyphse, bear- 
ing sporangia. The modes of reproduction in this plant are illus- 
trated in Fig. 548. 

Bread Mold (Rhizopus nigricans) is another member of this 
order. It produces fluffy mycelia on the surface of bread, fruits 




4 

■ Fig. 548. — Muco mucedo. a, a portion of vegetative mycelium, bearing an 
aerial hypha, terminated by a sporangium, b; b', sporangium more highly magni- 
fied, showing the contained conidia ; c, columella ; d, conjugating mycelial fila- 
ments, with a zygospore formed between. 



and other favorable substances when these are freely exposed to 
air. The sporangia are dark in color and give a black appearance 
to the mature mold. 

The Squirting Fungus (Pilobolus crystallinus) hurls its spor- 
angia with considerable force toward the light. It is common on 
manure. 

The Entomoplithoracesc, which are parasitic upon living insects 
of various kinds, are also classed here. Of these Empusa mus- 
cornm, which infests house-flies, destroying them in large num- 
bers, and EntomopJithora sph&rosperma, which often destroys the 
larvae of the Cabbage-butterfly, are common examples. The white 
sporangia of the former are often seen as a halo around dead flies 
on window panes. 

The Peronosporales or Downy Mildews are mainly parasitic on 
terrestrial Phanerogams; a few, however, as some of the species 
of Pythium, are saprophytic, feeding upon dead animal and vege- 
table matters. They produce unsegmented hyphse which ramify 
in the intercellular spaces of their hosts and, sending haustoria 



CHAPTER VI. — THE PHYCOMYCETES, OR ALGAL FUNGI. 343 

into adjacent cells, absorb nourishment from them. The great 
majority, after a time, send hyphse to the surface, frequently out 
through the stomata of the plant, and these bear sporangia which 
are shed, when ripe, in, the same manner as conidia, and hence are 
commonly so called, though they differ from them in the fact that 
when they fall into water, the contents break up into several 
rounded masses which escape as zoospores. These, after finding 
a lodgment on the epidermis of the host-plant, come to rest and 
produce hyphse, which either penetrate the walls of the epidermal 
cells or find their way into the interior through the stomata. A 
few of the forms, however, produce true conidia which give rise to 
hyphse directly; a few others neither produce conidia nor 
sporangia. 

Nearly all the species reproduce sexually by means of oogonia 
and antheridia. The oogonium formed at the end of a hyphal 
branch is similar in structure to the corresponding organ in the 
oosporous Algae, but the antheridia consist of one or more slender, 
curved out-growths, from the branch beneath the oogonium, or 
sometimes from adjacent hyphse. Both oogonium and antheridium 
are formed within the tissues of the host. In fertilization the 
antheridium applies itself directly to the surface of the oogonium, 
and usually a tube from it penetrates to the oospore and fertilizes 
it. In most cases the oospores rest for a considerable period before 
germinating, and then, in some cases, develop a mycelium directly, 
in others they first produce a germ-tube which develops one or 
more sporangia which gives rise to zoospores, and these, in turn, 
to a vegetative mycelium. 

To the Peronosporales also belong Phytophthora infestans, a 
blight which attacks the leaves, stems and tubers of the Irish 
Potato and is very destructive; Plasmopara viticola, the Grape- 
mildew, a most destructive Fungus, and Cystopus candidus, a mil- 
dew found on the Shepherd's-purse, and some other Cruciferous 
plants. 

Some idea of the modes of reproduction in this group may be 
obtained from Figs. 549 and 550. 

The Saprolegniales, or Water Molds, are aquatic fungi which 
form a dense mycelium on the bodies of animals that decay in 
water, and sometimes also upon submerged vegetable matter. 
They also attack young fish, through the gills, and often cause 
heavy losses in fish hatcheries. They resemble the Peronosporales 
in many respects, but differ from them in the fact that the spor- 



344 



PART IV. — TAXONOMY. 



angia produce ciliated zoospores, and that the oogonia produce 
several egg-cells instead of one. 

A curious and suggestive fact connected with some of the spe- 
cies of this group is, that while oogonia and oospores are produced 




Fig. 550. 



Fig. 549. 

Fig. 549. — Portion of epidermis of Potato, showing three stomata with hyphae 
of Phytophthora infestans issuing from them and bearing sporangia, a. one of 
the sporangia. Magnification about 100 diameters. 

Fig. 550. — Stages in reproduction of Peronospora Alsinearum. A. earlier 
stage, fertilization-tube of antheridium, a, not yet fully formed ; B, the tube 
fully formed and the fertilization of the oogonium, o, completed. Magnified 
about 350 diameters. After DeBary. 



as in the rest, either antheridia are not produced at all, or these 
do not perform the usual function of fertilization. The sexual 
process has in fact degenerated into an asexual one. This phe- 
nomenon is termed parthenogenesis, meaning reproduction by an 
egg without fertilization, and is particularly observed in the genus 
Saprolegnia, and, as we shall presently see, is a common one 
among the higher groups of the Fungi. 

Achlya lignicola, which feeds upon decaying, submerged wood, 
illustrates well the perfect forms of the group. See Fig. 551 A 
and B. 

THE CHYTRIDIACEjE. 

In this order are Fungi of the simplest organization, most of 



CHAPTER VI. — THE CHYTRIDIACEjE. 



345 



them being unicellular, and not producing hyphae, while a few 
of the higher forms produce rudimentary hyphae. They reproduce 
asexually by means of uniciliated zoospores. Sexual reproduction 
has been observed in but one species, and in this instance it takes 




frig. 551. — Achyla lignicola. A, Sporangia; a, sporangium nearly ripe but 
not yet dehiscent; b. sporangium dehiscing; z, zoospores; B, stages in sexual 
repn duction. In 1. the oogonium, o, and the antheridia, a, a. not yet fully 
formed ; 2, later stages when oogonium is nearly ready for fertilization ; 3, pro- 
cess completed and antheridia withering away. Magnified about 300 diameters. 

place by conjugation. In the typical genus Chytridium, the plants 
are unicellular, and their habitat is the interior of the living or 
dead tissues of aquatic Fungi and Algae. The cells, on reaching 
maturity, become sporangia and emit zoospores, which again 
germinate in the same plant, or, escaping, find their way to others 
and there germinate. See Fig. 552. 

THE ASCOMYCETES OR SAC FUNGI. 



This order consists of saprophytic or parasitic hyphal fungi, 
which produce a multicellular mycelium and on the whole attain 
a complexity of structure exceeding that of any of the groups 
already described. A few, however, as the Yeast-plant and its 
allies, are among the simplest of vegetable organisms. Some ef 



346 



FART IV. — TAXONOMY. 



them reproduce by means of conidia, and these may be formed 
from hyphse by the separation of cells in succession from their free 
ends, or they may be produced in special receptacles. But their 
most distinctive characteristic is the production of ascospores. 
These are spores formed in an ascus or sac. The. spores are usually 
eight in number, but in some species there are but two, and, in 
others, four or five. They have a thick outer wall and a thin 
extensible inner one. When placed under conditions favorable for 
germination, the outer wall bursts and the inner extends to form 
one or more tubes, from which the hyphse develop. 




Fig. 552. — Chytridium Olla. A, oogonium of (Edogonium rivulare, with an 
immature oospore killed by the parasite ; the oospore contains several resting- 
spores of Chytridium, which ripened in October; three of these spores are still 
unchanged ; two have germinated. By turning the specimen around, it was seen 
distinctly ' that the empty sporangium, a, was formed from the resting-spore a', 
and the sporangium b, which is ejecting its contents, from b' ; near the mouth of 
b, are the cast-off lid and two zoospores. Magnified 600 diameters. Figure and 
description after De Bary. 



Ususally the asci are produced in a specially developed organ 
or ascocarp, which is often a complex structure constituting the 
most conspicuous part of the plant, and may be cup-shaped, flask- 
shaped or globular: but in a few forms the asci are isolated, and 
not borne in a special f ruiting-organ ; and in other cases the latter 
is present, but has the simplest possible structure, sometimes 
merely the enlarged end of a hypha forming a thin-walled sac. 
Normally, the production of an ascocarp and ascospores, is the 
result of an antecedent sexual process analogous to that which 
occurs* in most Phycomycetes, but this is not always the case; in 
a large number of instances the organs of sexual reproduction 



CHAPTER VI. — THE ASCOMYCETES, OR SAC FUNGI. 



147 



either exist only in a rudimentary condition, or have entirely 
disappeared. 

When sexual reproduction occurs, it takes place by means of an 
ascogonium and an antheridium, the former corresponding to the 
oogonium of the Peronosporales, but differing from it in the fact 
that no oospores are developed within it, as well as in the fact 
that the collateral growths resulting from fertilization are usually 
very different. 




Fig. 553. — Penicillium glaucum. a. mycelium; b, 
conidia-bearing hypba ; c, conidia. Magnified about 
150 diameters. 

In some of the simpler species, the end of a hyphal branch 
becomes enlarged and ellipsoidal in form, and is separated from 
the rest by a septum to form the ascogonium, and an adjacent 
branch becomes less thickened, has its apical portion separated 
from the rest by a septum in a similar manner, and becomes an 
antheridium. In most cases, however, the filament that forms the 
ascogonium becomes twisted into a spiral, and covered, perhaps, 
by an out-growth of adjacent hyphae to form a compact mass. 
This may be provided with a projecting filament, or trichogyne, 
which receives the fertilizing influence, or it may be without it. 

In the species which do not produce a trichogyne, the anther- 
idium becomes entangled with the coiled filaments of the asco- 
gonium, and thus fertilizes them; in the species that do produce 
one, the antheridium, when ripe, discharg-es sperm cells which, by 
adhering to the trichogyne, fertilize the ascogonium. 



348 , PART IV. — TAXONOMY. 

The principal divisions of the Ascomycetes are the Erysiphese, 
the Plectascales, the Pyrenomycetes, and the Discomycetes. Here 
also are placed the Saccharomycetes or Yeast-fungi, and the appar- 
ently related Exoasci. 

The Erysiphese or Perisporiales include the Powdery Mildews, 
the mycelium of which forms powdery spots, thereby differentiat- 
ing this fungus from the Downy Mildews belonging to the Phyco- 
mycetes. Several species are common on the leaves of lilacs, 
apples, roses, alders, hops and other plants, and may do consider- 
able damage. 

The Plectascales include the Blue Molds an 1 . Green Molds, which 
superficially resemble the Black Molds (belonging to the Zygo- 
mycetales), but which produce greenish instead of blackish spore- 
masses. They occur along with the Black Molds, but have a wider 
range and are common upon cheese, leather, fruits and other 
objects that become "moldy" when damp. Aspergillus is a familiar 
Green Mold, common on preserved fruits. Its mycelium is loose 
and spreads through the substratum, sending up hyphae (conidio- 
phores), which bear conidia in chains at their ends. The sex 
organs appear later and consist of two short hyphal filaments 
which come together and intertwine. A cleistothecium, or closed 
case, results from their fertilization, and this contains asci with 
eight spores mingled with sterile hypha?. Upon the decay of the 
cleistothecium, the ascospores are scattered by the wind. 

Blue Mold, Penicillium glaucum, is common upon bread, often 
mingled with Black Mold. The conidia are borne as shown in 
Fig. 553. Its ascosporous fructification is similar to Aspergillus. 
The peculiar flavor of Roquefort, Camembert and other cheeses 
is due to species of Penicillium. 

The Pyrenomycetes are characterized by producing a compact 
superficial mycelium of dark color suggesting charring by fire, 
hence the name, literally "burnt fungi." They form the familiar 
black swelling on Cherry and Plum trees, which they injure 
severely. The mycelium develops parasitically in the bark and at 
length breaks through as a black, swollen prominence or sclero- 
tium. Hyphae arise from this and bear conidia, which are scat- 
tered by the wind, thus spreading the infection. In the next stage, 
the knot bears club-shaped asci in the interior of roundish or 
flask-shaped ascocarps, or perithecia, and these are distributed 
early in the spring, thus carrying the disease to new hosts. 

Chestnut blight {Endothia parasitica) , which was introduced 



CHAPTER VI. — THE ASCOMYCETES, OR SAC FUNGI. 349 

into this country a few years ago and has been very destructive 
to chestnut trees; Cordyceps, whose various species are parasitic 
upon the bodies of insect larvae; and Claviceps, whose species pro- 
duce ergot on various kinds of grasses, belong to this group. 
Claviceps purpurea, which constitutes, in one stage of its develop- 
ment, Ergot of Rye, may be selected for more particular descrip- 
tion. The ascospores of this fungus infect the ovaries of the Rye 
when it is in flower, and appear as a tangled mass of delicate 
mycelial threads on the surface of the ovary, also penetrating its 
tissues. 

These mycelial threads develop numerous conidia and at the 
same time produce a sweet liquid, or "honey dew," which attracts 
insects, who carry the conidia to other flowers and rapidly spread 
the disease. There then begins to form, at the base of the diseased 
ovary, a dense mass of mycelium, which continues to enlarge 
until it forms the hard, dark-purple, club-shaped sclerotium, the 
medicinal Ergot. 

The remains of the upper part of the ovary and the style are 
often seen attached to the apex of the sclerotium, even when the 
latter is mature, but it very soon afterwards falls off. Sometimes 
as many as twenty sclerotia are produced in a single diseased 
head of Rye, but more commonly not more than two or three. 
Each sclerotium consists wholly of a hard and compact mass of 
mycelium, and contains no part of the original grain of Rye 
which it has displaced. This sclerotium lies dormant until spring, 
when, if placed in warm, damp soil, there arise from its interior 
a number of stalked bodies with rose-colored globular heads. These 
are the stromata^and each contains just beneath its convex surface 
numerous flask-shaped perithecia, each of which contains many 
asci, and each ascus contains several delicate thread-like asco- 
spores. 

At maturity the asci rupture and discharge the spores, which, 
if they find their way to the young flowers of Rye, germinate and 
produce the mycelium, with which this description started, and 
so the cycle is completed. The successive steps in the reproduc- 
tion of this Fungus are illustrated in Figs. 554 to 559, inclusive. 

The Discomycetes differ from the rest of the group chiefly in 
the structure of the hymenium, which is on the surface of a 
discoid, cup-shaped or club-shaped fructification, which may or 
may not be the result of an antecedent fertilizing process which 
takes place in the mycelium growing in the substratum. Some 



350 



PART IV. — TAXONOMY. 




Fig. 559. 

Fig. 554. — Head of Rye, bearing three Ergot-grains. 

Fig. 555. — Pistil of Rye attacked by Ergot blight — Claviceps purpurea, in the 
first or sphacelial stage of development. Somewhat magnified. 

Fig. 556. — Ergot-grain after lying over winter, producing stromata. Nearly 
natural size. 

Fig. 557. — A fructifying organ or stroma of Ergot in longitudinal section, 
magnified, a, a. perithecia imbedded in the margin. 

Fig. 558. — A perithecium much more highly magnified, showing the club- 
shaped asci in its interior. 

Fig. 559. — One of the asci greatly magnified, shown in the act of discharg- 
ee its ascospores. The discharge really takes place from the ascus, before it 
ltaves the perithecium. 



CHAPTER VI. — THE ASCOMYCETES. OK SAC FUNGI. 



351 



of the forms are parasitic, others saprophytic. The group includes 
the largest and most highly developed members of the Ascomycetes. 
Here belong the Pezizales or Cup-fungi, common in woods, growing 
upon leaf-mould and producing a cup-shaped apothecium ; the 
Helvellalex, including Morchella (see Fig. 566), Helvella, etc., 
which have large, mostly club-shaped ascocarps, the hymenium of 
which is borne either on a smooth or on a reticulately indented 
surface; and the Phacidex, which produce small, blackish, disc-like 
or roundish fructifications on dead leaves of various kinds. 

The fungus parts of most Lichens also belong in this group, but 
owing to the composite character of these plants they had best be 
considered separately. 

For a fuller illustration of the life history of these plants we 
may take Py rone ma confluans. The mycelium grows in soil rich 
in organic remains and sends up ascending hyphse which develop 
numerous oogonia tipped with stout trichogynes. Into contact with 
these grow the antheridia developed from other hyphal cells. 
After the fertilization is effected, the oospores grow new hyphae 
from which are developed the asci, until a mass of considerable 
size is formed; on the upper surface is developed a hymenial layer 
of closely compacted erect hyphal branches; the whole apothecium 
gradually assumes the form of a cup. The ripe ascospores are 
shed by the rupture of the asci and are disseminated by the wind. 




Fig. 560. — Sexual reproduction in Pyronema confluans. A, the sex organs 
at the time of fertilization, showing the antheridia (a) in contact and fusing 
with the trichogynes through which the sperms pass to the oogonia (o) ; B, 
development of apothecium, showing the oogonia developing ascogenous hyphae 
which are beginning to form asci at the ends of their branches, and the sterile 
hyphae (b) which grow up among the ascogenous hyphae and form a large part 
of the wall of the apothecium. Highly magnified. (After Harper from Martin.) 



352 PART IV. — TAXONOMY. 

The Tuberales arc, many of them, highly prized for food, under 
the name of Truffles. They produce subterranean, tuber-like asco- 
carps from a mycelium that penetrates through the soil, and, in 
some instances, appears to form a mycorrhiza with the roots of 
certain trees. The ascocarp is usually spherical, and invested 
with a tough cortical layer. The ascospores are produced in 
intricately winding passages in the interior. Each ascus contains 
from two to four spores, which are set free by the decay of the 
surrounding parts. Since these tuber-like fructifications are 
formed underground, they are hunted by means of pigs or dogs, 
which detect them bv their aromatic odor. 





Fig. 561. — Yeast cells, a, cells of Saccharomyces Cerevisiae, not budding; 
b, budding cells of tbe same plant ; c. cells of S. ellipsoideus developing ascospores. 
All magnified about 700 diameters. 

The Saccharomycetes, or yeasts, as has already been stated, aro 
now classed among the Ascomycetes and are regarded as degen- 
erate members of the group. They include most of the forms 
which are capable of exciting the alcoholic fermentation in sac- 
charine liquids. They are minute plants of very simple structure, 
consisting of rounded or ellipsoidal cells, which either occur singly 
or loosely united into short chains. The cells contain cytoplasm, 
a nucleus and a vacuole, and, when growing in a suitable medium, 
they increase rapidly by budding or sprouting. This is their prin- 
cipal and, under ordinary circumstances, their only mode or 
increase, but when deprived of sufficient nourishment, as for exam- 
ple when wine-ferment is cultivated for several days on a porous 
tile kept moist under a bell- jar, the cells cease sprouting and the 
contents break up into four ascospores, which develop thick walls 
and pass into a resting stage. 

In this stage, they are carried through the air, as dust, and are 



CHAPTER VII. — THE BASIDIOMYCETES, OR BASIDIA FUNGI. 353 

found everywhere. Yeasts are readily cultivated on suitable media 
and, as the flavor of the fermented products depends in large 
measure on the yeast, pure cultures of certain kinds are much 
used. In fact, yeast is one of the oldest of cultivated plants. 
Brewer's yeast (Saceharomyces cerevisise) is familiar, especially 
as "compressed yeast," in which form it is largely used in making 
bread. The manufacture of beer, wine and other alcoholic liquids 
depends upon yeasts. Saceharomyces ellipsoideus or wine yeast 
is a wild yeast which gains access from the skins of the grape to 
the grape juice. 5. albicans is pathogenic, causing the disease 
known as "thrush." Cells of common yeast are shown in Fig. 561. 
The Exoasci are another group of very simple and apparently 
degenerate Ascomycetes. They possess no ascocarp and the asci 
are borne exposed. They are parasitic upon Spermatophytes. One 
species attacks the leaves of the Peach, causing "Peach Curl," 
another grows on the young ovaries of the Plum, causing the 
deformity known as "Bladder Plums." A third produces the 
so-called "Witches Brooms" on some of our deciduous trees. Sex- 
ual reproduction is unknown in this group. 



CHAPTER VII.— THALLOPHYTA.— FUNGI (Continued). 



THE BASIDIOMYCETES.— THE USTILAGINALES.— THE 
FUNGI IMPERFECTI. 



THE BASIDIOMYCETES, OR BASIDIA FUNGI. 

The distinctive characteristic of this group is the fact that at 
the ends of the spore-bearing hyphae, large, club-shaped or oblong 
cells are produced which bear at their apex delicate processes, two, 
eight or, more commonly, four in number, each of which is ter- 
minated by a rounded or ellipsoidal spore. The cells which bear 
the spores are called basidia, and the spores, basidio spores. The 
basidia occur in large numbers compactly arranged, sometimes 
with intervening sterile filaments called paraphyses, on or in a 
definite part of the sporocarp, constituting the hymenium. The 
sporocarp is usually of considerable size, forming much the most 



354 PART IV. — TAXONOMY. 

conspicuous part of the plant, the vegetative mycelium, in fact, 
being usually concealed in the substratum. The spores in the 
hymenium all ripen about the same time, and then the sporocarp 
usually withers away or decays. 

The Basidiomycetes are classified scientifically according to the 
shape of the sporocarp, the position and character of the hyme- 
nium, the position of the teleutospores, etc. One species, Exobasi- 
dium vaccinii, shows a very simple fructification, consisting of 
compactly arranged basidia forming a hymenium directly on the 
surface cf the organs which it attacks. The plant is a parasite 
on the leaves and stems of V actinium vitis-idsea. The Basidiomy- 
cetes are distributed into four groups: The Uredinales or Rusts, 
the Ustilaginales or Smuts, the Hymenomycetes or Mushrooms, 
and the Gasteromycetes or Puffballs. 

The Uredinales are popularly known as Rusts, and are parasites, 
forming yellowish, brownish or blackish spots on the stems and 
leaves of various plants. Some of them, as the Wheat-rust, are 
highly destructive to crops. The name JEcidiomycetes, sometimes 
applied to these fungi, refers to a peculiar form of fructification 
called "aecidia," which are produced by the species. iEcidia consist 
of a cup-shaped envelope or peridium, in the bottom of which rows 
of cells are formed and separated one after the other, by transverse 
division, forming rounded spores called secidiospores. They are 
only a pecular form of conidia, and the whole fructifying organ 
corresponds, doubtless, to the ascocarp of the Ascomycetes. 

In some species, the secidiospores, on germinating, produce 
short, few-celled filaments, constituting a promycelium which soon 
ceases its vegetative growth and bears small conidia, called 
sporidia. These, when deposited by the wind or some other agency 
on a suitable host-plant, germinate and produce tubes which pene- 
trate the epidermis or enter the stomata and develop a mycelium 
in the interior of the host-plant, and this mycelium again produces 
aecidia. 

In some of the species, however, the life-history is more com- 
plex, there being two distinct stages in it that are spent on differ- 
ent host-plants, and in which different sets of reproductive spores 
are developed. Of this group, the common Wheat Rust, or Black 
Rust, Puccinia graminis, may be taken as an illustration. This first 
makes its appearance in the form of rust-colored patches on the 
stems and leaves of Wheat and other grasses. These spots are due 
to multitudes of reddish spores, called uredospores or "summer 



CHAPTER VII. — THE BASIDIOMYCETES, OR BASIDIA FUNGI. 355 

spores," produced from a mycelium growing within the plant. 
These spores are produced abundantly and are dispersed by the 
wind; if the season is damp and warm the infection rapidly 
spreads from plant to plant and great damage is done. 

Spore production of this kind continues until toward the close 
of the growing season, when, as the grain is ripening, the rust-like 
patches change to a darker, almost blackish color. This is due to 
the development of another kind of spores called teleutospores or 
"winter spores," which differ from the others in being two-celled 
and having thicker walls. Moreover, they are not capable of 
developing on a healthy blade of grass, but rest over winter in 
the straw, and in the spring germinate, producing a promycelium, 
the branches of which bear the basidiospores, or sporidia. These 
are wafted away by the winds and germinate on the leaves of the 
Barberry and, perhaps, on other plants, but not on the Wheat. 
These immediately produce hyphae which, penetrating the stomata, 
form a mycelium which derives nourishment from the cells of the 
leaf, and finally bursts through the epidermis on the under surface 
of the leaf and forms the secidia popularly known as "cluster- 
cups." 

In these little cups are formed multitudes of small, rounded, 
yellow or orange-colored aecidiospores which the wind scatters. 
These do not germinate on the Barberry, but those which are 
conveyed to the leaves of grasses develop hyphae, which penetrate 
to the interior of the leaf, and after a time produce the rust-like 
patches at the surface. 

At the same time as the sescidia are produced, there are usually 
formed on the upper surface of the Barberry leaf, small flask- 
shaped structures or spermagonia containing functionless sperma- 
tid, supposedly representing sexual spores. 

Some of the steps in the reproduction of this plant are shown 
in Fig. 562, A, B and C. 

This remarkable life-cycle of Wheat Rust, including four kinds 
of spores, besides the spermatia, and affecting two host-plants, is 
of great economic interest. No effective method of combating the 
rust has been found, for even the destruction of the Barberry does 
not eradicate the disease. While the uredospores are usually killed 
by freezing in winter weather, yet they can survive in the young 
plants, where Winter Wheat is grown, and then reinfect the fields 
in the spring. The best remedy seems to lie in the selection and 
cultivation of varieties of Wheat that are resistant or immune to 



356 



PART IV. — TAXONOMY. 



the Rust. Black Rust also infects Oats, Rye, Barley and other 
Grasses. 

The phenomenon of alternating stages on different hosts, so 




Fig. 562. — Puccinia graminis. A, part of a thin cross-section of Barberry 
leaf showing four aecidia, a, a, a, a, in various stages of development on the 
under surface, and four spermagonia, sp, imbedded in the upper surface. B, 
group of ripe teleutospores bursting through the epidermis, e, of a leaf of Trit- 
icum repens. C, Uredospores. r, and teleutospore, t, more highly magnified. 
A, slightly magnified; B, magnified about 190 diameters, and C, magnified about 
390 diameters. After Sachs. 



prominent in this group, also occurs in some others and is likewise 
exemplified in some of the lower forms of animal life. 

Gymnosporangium juniperi-virginianse. produces the gall-like 
growths knows as "Cedar apples" on the leaves of the Red Cedar. 
Its cluster cups appear on the leaves and fruit of the Apple 
(Malus) and constitute the disease known as "Apple Rust." Other 



CHAPTER VII. — THE USTILAGINALES, OR SMUTS. 357 

Rusts attack Asparagus, Peach trees, Pine trees and other plants, 
causing serious damage. 

THE USTILAGINALES. 

The Ustilaginales or Smuts, of which the common Corn-smut, 
J T x(ilago Maidis, may be taken as the type, are parasitic upon 
flowering-plants, chiefly on the Grasses, and cause much damage 
to the cultivated cereals. The slender mycelial threads usually 
penetrate through the intercellular spaces of the host-plant, and 
in some species send sucker-like branches (haustoria) into its 
cells. In some instances the parasite attacks the seedling plant and 
sends its hyphae through the whole structure, growing as it grows ; 
in others it attacks the more mature plant, and confines its ravages 
to certain parts. 

At maturity it produces, either at the outside of the host-plant, 
or in its intercellular spaces, very numerous chlamydospores on 
tangled mycelial filaments. These most frequently occur on the 
inflorescence, or on parts adjacent to it, and the spore-masses, 
together with the abnormal growth caused by it, often assume 
quite characteristic forms. Corn-smut forms irregular, roundish- 
lobed masses, often attaining a diameter of six inches or more. 
The masses consist of a translucent gelatinous membrane enclosing 
innumerable blackish-brown, rounded "brand" spores, having a 
nodular surface and a thick wall. These chlamydospores survive 
the winter, either on the ground or in the straw, or in the grain 
itself. They germinate the following spring, giving rise to a pro- 
mycelium, regarded as a basidium, and on which basidiospores are 
produced which develop into a true mycelium. 

The Smut of Oats, Stinking Smut of Wheat and Covered Smut 
of Barley are due to similar fungi. 

The Gasteromycetes are distinguished from the rest of the Fungi 
by the fact that the hymenium is enclosed within the peridium or 
body of the sporophore. The latter may be uniform or it may be 
differentiated into two coats, the outer and inner peridium and the 
interior, known as the gleba, variously subdivided into compart- 
ments, on the walls of which the basidia are borne. In many 
species the number of spores on each basidium is eight, but in 
some there is the usual number, four. 

By reason of the complex structure of their sporophores, the 
Gasteromycetes are usually considered the highest of the Fungi 
in development. They are often found growing with the Mush- 



358 PART IV. — TAXONOMY. 

rooms, requiring about the same conditions for growth, and, like 
the latter also, many species are edible. 

The hy coper dace x, the Hymenogastracese, the Nidulariacese and 
the Phallacese, form the sub-divisions of the group. 

The Lycoperdacese include the Puff-balls and Geasters or Earth- 
stars. The rounded sporophores of the former produce innumer- 
able brown spores, which are discharged in clouds by the scaling 
away of the outer peridium and the rupturing of the inner one. 
The latter are similar, except that the tough outer peridium sep- 
ates hygroscopically into regular segments, which flatten out into 
a star-like form. (Fig. 565.) 

The Hymenogastracex are subterranean fungi, resembling, in 
their habits, the Truffles. In most of the other species of the group 
the walls of the chambers, constituting the supporting frame-work 
for the hymenium, undergo great changes during the development 
of the sporocarp, for example, in the Lycoperdons the chambers 
disappear, leaving only a loose frame-work of threads; but in the 
species of this group they remain unchanged until the ripening is 
complete. The spores are finally set free by their decay. 

The Nidulariacese or Bird's-nest Fungi (see Fig. 564) , form 
small cup-shaped sporophores. When ripe the peridium opens at 
the top, exposing several rounded hard bodies, peridiola, which 
look something like eggs in a nest. These bodies are the spore- 
bearing chambers of the gleba which have become isolated in the 
process of development. 

The Phallacese, or Carrion Fungi, are at first rounded, but in 
development, the peridium, which consists of three layers, bursts 
and exposes a chambered gleba which is elevated on an elongating 
stalk. The hymenium soon becomes a dark-colored and foul-smell- 
ing mucilaginous mass in which the spores are inclosed. The 
spores are scattered by carrion-flies, which are attracted to the 
plants in large numbers by the smell. 

The Hymenomycetes include such familiar Fungi as the Mush- 
rooms and Toadstools. They are a numerous and important 
group, resembling each other in the fact that at the time the spores 
are ripe, the hymenium, which consists of basidia associated with 
sterile hyphae, occupies the outer free surface of the sporophore or 
fruit-body and not its interior. 

The fungi of this group are usually saprophytic in habit, the 
showy sporophore developing from an invisible mycelium, which 
may be hidden in the ground or in dead tree trunkg. Only a few 



CHAPTER VII. — THE USTILAGINALES. OR SMUTS. 359 

are parasitic and may attack living trees. The species bearing 
sporophores of umbrella-like form with stalk, cap and gills, are 
popularly known as Toadstools or, when edible, Mushrooms, 
although the latter term is often applied to edible fungi of other 
groups. Some of the Toadstools are very poisonous, others are 
merely tough and unsuited for food. 

According to the shape of the sporophore and the structure of 
the hymenium, several sub-groups are distinguished, among which 
are the following: 

The Thelephoracex, or Leather Fungi, are, in their structure, 
the simplest of the group. In all the hymenium is smooth. They 
form incrustations, in some species of irregular, in others of regu- 
lar form, on logs, the barks of trees, etc. Exobasidium attacks the 
ovaries of flowers of the Heath family, producing gall-like growths. 

The Clavariacex, Club-fungi or Coral Fungi, a related form 
(see Fig. 567), have cylindrical or club-shaped, simple or branch- 
ing sporophores, which may, according to the species, be white, 
gray, brown or yellow in color. The hymenium occupies the smooth 
exterior surface, and when the spores are ripe, they communicate 
to it a dusty appearance. 

The Hydnacese or Tooth Fungi (see Fig. 568) are distinguished 
from the rest by the fact that the hymenium consists of prickle-like 
projections from the surface of the sporophore. There are many 
species, some of them having a cap or pileus supported by a central 
stalk, as in the common Mushroom; sometimes the stalk is attached 
laterally, and sometimes there is no stalk. 

The Polyporacese, Pore Fungi, are characterized by producing 
a hymenium which consists of straight tubes arranged compactly 
side by side. On the inner surface of these tubes the spores are 
borne. The hymenium covers the under surface. Some of the 
species produce fructifications of large size. In the genus Poly- 
porus, the Bracket Fungi, they mostly form lateral, shelf-like 
projections often seen on dying trees. The mycelium spreading 
through the wood gradually reduces it to a pulp and kills the tree. 
In the genus Boletus (see Fig. 569), there is an expanded cap and 
a stalk, the latter usually placed centrally. The tough, spongy 
mycelium of Polyporus fomentarius is sometimes used in surgery 
under the name of Surgeon's Fungus, and, saturated with solution 
of potassium nitrate and dried, it constitutes what is called Spunk 
or Punk. Polyporus officinalis, a parasite upon the European 
Larch, has medicinal properties, and Boletus edulis is one among 



360 PART IV. — TAXONOMY. 

the few of the large genus to which it belongs, that is prized for 
food. 

The Agaricacew, the Agarics or Gill Fungi, produce a sporo- 
phore which is commonly expanded and hat-like in form, and in the 
majority of cases, is supported on a central stalk; but sometimes 
the latter is inserted to one side of the center, or in a few species 
is altogether wanting. The most distinctive features of the group, 
however, consist in the structure of the hymenium, which is com- 
posed of lamelliform bodies, or "gills," as they are often called, 
arranged in a radial manner on the under surface of the expanded 
umbrella-like portion of the sporophore or pileus. Many of the 
stalked forms are, in the early stage of their development, invested 
with a membrane called a velum or veil, which, at a later period, 
is ruptured; but its parts usually remain in the mature sporophore, 
forming a sheath at the base of the stalk, or a ring around it 
higher up, or fringing the border of the pileus. Other forms are 
destitute of this membrane. 

The species are numerous, many of them edible, others uselesc 
for food, and still others highly poisonous. Among the latter may 
be mentioned the Deadly Amanita, from which the alkaloid mus- 
carine is obtained. Several species are brightly and beautifully 
colored. Some, as the genus Coprinus, produce a very perishable 
sporophore, others are hard, leathery and enduring. The genus 
Lactarius is distinguished from the rest, and from most § other 
thallophytes, by possessing a milky juice. Commonly, the hyme- 
nium is borne on the under side of the sporophore and is thus 
protected from rain. 

For further illustration of the group, we" may select Agaricus 
campestris, the common Mushroom. A mass of mycelium called 
by mushroom growers "spawn," is formed by the germinating 
spores in the vegetable mold or humus, from which the plant 
absorbs its food. On this mycelium protuberances of a rounded 
or nodular form, popularly known as "buttons," sooner or later 
make their appearance and rise above the soil. These are the 
young sporophores still invested in their membrane. Presently 
the membrane or veil ruptures, exposing an upright stalk or stipe 
composed of compactly arranged hyphae, which are continued at 
the top into the pileus. The latter is convex and nearly smooth 
above, and the numerous radiately arranged, plate-like gills, cover 
the concave surface below. The gill surfaces are composed partly 
of large sterile cells, and partly of basidia, and each of the latter 



CHAPTER VII. — THE FUNGI IMPERFECTI. 



361. 



bears two spores. The spores are minute, and the aggregate 
number produced by a sporophore is enormous. 

In this species a portion of the velum remains as a ring or 
unnulus on the stalk. See Fig. 563, A, B and C. 




Fig. 563. — Agaricus compestris. A, two sporophores, one of them, b, quite 
young, and still enclosed in its membrane, the other fully matured ; a, the 
"gills" or hymenium ; n, the annulus. Somewhat reduced. 

B, young sporophores, s, s, of the same species, showing how they originate 
from the mycelium, m. 

C, a small portion of one side of one of the gills of the same fungus, show- 
ing basidia b, and sterigmata, d. Magnified about 325 diameters. 

Figs. 564 to 571 illustrate various species of the higher Fungi. 

In the genus Amanita the veil covers the whole fruit-body and 
when it is ruptured during growth the lower part remaining 
attached to the base of the stalk forms the volva or "death cup." 
Fig. 570. 

THE FUNGI IMPERFECTI, OR IMPERFECT FUNGI. 

Here are included a large group of Fungi, numbering about 
16,000 kinds, whose life histories are imperfectly known. As this 
group is an artificial one, formed only for convenience in classifi- 
cation, its membership is constantly changing, for as investigation 
goes on the life histories of its members are worked out and they 
are properly classified elsewhere. While the group is thus a 
heterogenous one, its fungi differing greatly in their characteris- 
tics, yet their resemblances are chiefly to the Ascomycetes. 

Reproduction is commonly from conidiospores and the manner 
in which these are borne affords the usual basis for the classifica- 
tion of this group. 



362 



PART IV. — TAXONOMY. 




Fig. 571. 



CHAPTER VIII. — THE LICHENES, OR LICHENS. 363 

While the larger number are saprophytes, there are also many 
parasites, some of these producing serious diseases on cultivated 
plants, such as Apple Blotch, Late Blight of Celery, Leaf Blight 
of Tomato, Anthracnose of Grape, Early Blight of Potato and 
Black Rot of Sweet Potato. 



CHAPTER VIII.— THALLOPHYTA.— FUNGI (Continued). 



THE LTCHENES, OR LICHENS. 

These plants are here treated as a separate group more for 
convenience than because there is anything in their structure which 
warrants the distinction. Each is, in fact, an alga and a fungus 
living together as host and parasite. Lichens are therefore com- 
posite structures. A few of the fungi composing them belong to 
the Basidiomycetes, but by far the larger portion to the Ascomy- 
cetes, and in each case the modes of reproduction are such as 
characterize these groups respectively. 

The algae mainly belong to the unicellular Green Algse or some 
form of the Blue-green Algae, among others, the Nostocs, the 
Palmellas, Chroococcus, Chroolepus, and, more rarely, the Confer- 
voidae; and while they do not lose their power of vegetative multi- 
plication by reason of the parasitism, they do lose the power to 
reproduce by other means, and moreover, frequently undergo 
important structural modifications. They often occur free from 
the fungus association, but the lichen fungi are seldom found 
growing separately. 

The parasiticism of the fungus upon the alga, constituting the 
lichen, has been compared to that of master and slave (Helotism). 
It seems likely that the alga suffers little injury from the attack 



Figs. 564 to 571. — Fungi of various kinds. 

Fig. 564. — Cyafhus, one of the Nidularieae or Bird's-nest Fungi, slightly 
enlarged. 

Fig. 565. — Geaster. or Earth-star, nearly natural size. 

Fig. 566.— Morchella esculenta, one of the Discomycetes. 

Fig. 567. — Portion of Clavaria rugosa. one of the Hymenomycetes. 

Fig. 568. — Hydnum repandum, one of the Hymenomycetes, about two-thirds 
natural size 

Fig. 569. — Boletus edulis. one of the Polyporeae.. about half natural size. 

Fig. 570. — Agaricus muscarius. the Fly Agaric, about two-thirds natural 
size. 

Fig. 571. — Marasmus oreades. about two-thirds natural size. 



S64 



PART IV. — TAXONOMY. 



of the fungus and in fact is benefitted to a degree, since the hyphal 
cells of the latter help to retain water which enables the green 
algal cells to make carbohydrates under conditions of drought, 
which other plants could not survive. Lichens are therefore quite 
independent of food supplies in the substratum and can exist on 
bare rocks, the barks of trees, fence-rails and other exposed sur- 
faces. They are found everywhere, often acting as pioneers by 
aiding in the disintegration of rocks and the formation of soil and 
preparing the way for Mosses and other plants. 

Some idea of the character of this association between parasite 
and host may be gained by the study of Fig. 572 A and B, taken 




Fig. 572. — Portions of two Lichens, showing fungi parasitic on Algae. In 
A, the filaments, g, g, belong to a species of Scytonema and the hyphae, h, h, h, 
are those of Stereocaulon ramulosus. Magnification about 950 diameters. 

In B, a hyphal branch, h, is entering the cells of a species of Nostoc, g. 
Magnification about 650 diameters. Both after Bornet. 



from Bornet's researches on the Lichens. Here portions of tissue 
from two different Lichens are shown. 

It has been determined by experiment that the lichen alga 
freed from the lichen fungus can lead a normal life and may then 
be identified, even though this is not possible during its parasitism 
by the fungus which prevented its normal development. Lichens 
have been produced artificially by allowing the spores of the 
lichen fungus to germinate on free algae. By such synthesis, it 
has been learned that one algal species may serve several lichen 
fungi. With perhaps one exception, however, the latter are not 
able to grow except in symbiosis with their algal hosts. 

The colors of lichens vary from almost white to greenish-gray, 



CHAPTER VIII. — THE LICHENES. OR LICHENS. 



365 



yellow, orange or brown. Examined microscopically, their tissues 
always show colorless filaments, the fungus hyphae, and green or 
red chlorophyll-bearing cells which belong to the Algae. The latter 
are technically called gonidia. 

In some Lichens the algae are equally distributed throughout 
the thallus; in others they are arranged in definite groups or 
layers. The former kinds are described as homoiomerous, the latter 
as heteromerous. All the species are capable of enduring dessica- 
tion without destroying their vitality. 




Fig. 573. — Vertical section of apothecium of An- 
aptychia ciliaris ; h, hymenium, producing numer- 
ous asci ; g, gonidial layer ; r, rind, composed of 
compact hyphae ; m. medulla, composed of loosely 
arranged hyphae. Magnified ahout 50 diameters. 
After Sachs. 

The fructification of Lichens is, as we have seen, that of the 
fungus and not of the alga. The sex organs suggest those of the 
Red Algae. 

In the common Tree Lichen, the grayish and radiate thallus or 
plant body is composed of hyphal cells surrounding green algal 
cells and sending down thread-like rhizoids which serve to fasten 
the plant to its substratum, usually the bark of an old tree; as 
the hyphal cells spread, the algal cells multiply by cell-division 
and thus keep pace with the growth. On the surface of the thallus, 
there form many cup-like apothecia in the hymenium of which asci 
and paraphyses are formed as they are in the Discomycetes. 
These asci develop ascospores. 

In other species the apothecium is closed and the spores, when 
ripe, escape from a narrow opening, as in the Pyrenomycetes. 
Fig. 573 represents a perpendicula section of an apothecium of 
the cup-like kind. 

Many of the Lichens also multiply vegetatively by means of 
soredia. These are gonidia, or groups of them, wrapped about 



366 PART IV. — TAXONOMY. 

with hyphal filaments, which escape from the Lichen thallus, 
usually in the form of a fine powder, and germinate directly to 
form new plants. 

According to the structure and mode of growth of the thallus, 
Lichens may be described as: 

The Homoiomerons Lichens. The members of this group have 
for the most part a more or less gelatinous thallus, which is some- 
times flattened and lobed, and sometimes filamentous, consisting 
of an algal filament with fungus hyphse wrapped about it. Their 
algae all belong to the Cyanophycese. The remaining groups are 
Heteromerous or stratified. 

The Crustaceous Lichens form a numerous group, having a 
thallus of indefinite form adhering so closely to the substratum on 
which they grow, that it is often difficult to distinguish them from 
it. They grow on rocks, smooth-barked trees, wooden fences, and 
sometimes on the ground. 

The Foliaceous Lichens form flattened leaf -like expansions, 
which may be variously lobed or crisp ate on the margins, and 
adhere, often in the form of rosette-like patches, more or less 
closely to the substratum. Many of these, as the Parmelias and 
Stictas, form greenish-gray or yellowish patches on tree-trunks, 
fences, etc. ; others, as the species of Peltigera, grow on damp 
hillsides among the moss, and bear their apothecia on the lobed 
borders of the thallus. Still other species, as those of Gyrophora 
and Umbilicaria, form dark-colored patches on rocks. See Figs. 
574 and 575. 

The Fruticose Lichens have a shrub-like growth, often branch- 
ing profusely, and are attached to the substratum only at the 
base. The branches of the thallus are in some species cylindrical, 
in others flattened, but even in the latter there is usually little, if 
any, structural difference between the upper and under surface. 
For the most part the gonidia are arranged in the form of a hollow 
cylinder running lengthwise of the branches; the interior of the 
cylinder is filled with hyphse, and on the exterior they enclose it as 
a sheath. Many of the species cling to tree-trunks, logs or rocks, 
but some grow upon damp earth. 

To the forms having cylindrical branches belong the Usneas 
(see Fig. 576), Roccella tinctoria, a Lichen that constitutes one of 
the principal sources of Litmus (see Fig. 577), and the familiar 
Cladonia rangiferina, or Reindeer Lichen; and to those with flat- 
tened branches belong the so-called Iceland Moss, Cetraria islandica, 



CHAPTER VIII. — THE LICHENES, OR LICHENS. 



367 



prized as a food, and used in medicine for its demulcent and tonic 
properties. (See Fig. 578.) Several species yield red, purple, 
brown 01 yellow dyes. None are poisonous. 

Since the fungus is the ruling member of the composite struc- 




Fig. 576. 



Fig. s; 



Fig. 574. — Portion of thallus of Sticta pulmonacea, a foliaceous Lichen. 
a, apothecium. Natural size. 

Fig. 575. — Thallus of Umbilicaria vellea, a foliaceous Lichen, a. apothecium. 
Natural size. 

Fig. 576. — Thallus of Usnea barbata. a fruticose Lichen, about natural size, 
a, apothecium. 

Fig. 577. — Thallus of Roccella tinctoria. a fruticose Lichen, about natural 
size, a, apothecium. 

Fig. 578. — Portion of Cetraria islandica. a fruticose Lichen with a flattened 
thallus. About natural size. 



368 PART IV. — TAXONOMY 

ture, determining the form of growth, the classification of Lichens 
is usually based on the fungal constiutent and four families are 
recognized : 

Discolichenes, producing asci in apothecia, as in the Discomy- 
cetes; Pyrenolichenes, producing asci in perithecia in the manner of 
the Pyrenomyeetes ; Basidiolichenes, where the fungus belongs to 
the Basidiomycetes, and Gasterolichenes, where the fungus belongs 
to the Gasteromycetes. 



CHAPTER IX.— THE BRYOPHYTA, OR MOSS PLANTS. 
THE HEPATIC^E.— THE MUSCI. 

CHARACTERISTICS OF THE BRYOPHYTES. 

The Bryophytes, on the whole, show, in the more complete 
differentiation of their cells into tissues and of the plant body into 
stem, leaves and root-hairs, as well as in their more complicated 
reproductive process, a decided advance in structure over the 
Thallophytes. At first sight the two groups seem sharply distinct, 
but a closer comparison shows that there are few points in the 
Bryophytes which have not been clearly anticipated by some of 
the plants below them. In turn, the Bryophytes anticipate some 
of the features of the higher plants. 

The Bryophytes are the simplest of land plants. They are 
supposed to have originated from the Algae and to have been the 
most primitive of land plants. As contrasted with the Algae, which 
soon die when taken from the water, the Mosses are protected by 
their structure against too rapid transpiration. They are not 
parasitic and are seldom harmful; they have, however, but slight 
economic value. 

All Moss-plants are chlorophyll-bearing; in all, the plant body 
consists of true tissues formed by cell-division; all are of small or 
moderate size, seldom attaining more than a few inches in height, 
yet none of them at maturity are so small as to be strictly micro- 
scopic; none possess true roots, these being replaced by rhizoids, 
consisting of branched, thread-like cells by means of which they 
attach themselves to the substratum or absorb nutriment; a few 
are aquatic; most are either terrestial or epiphytic, but none are 
either parasitic or saprophytic. 



CHAPTER IX. — THE BRYOPHYTA, OR MOSS PLANTS. 369 

All the species are characterized by a distinctly-marked alterna- 
tion of a sexual with an asexual generation. The gametophyte or 
plant which bears the sexual organs is the more conspicuous; it 
may be either a leafy-stemmed plant or a thallus. 

In the majority of the Bryophytes, the distinction between leaf 
and stem is clearer than in the Characese and other foliose Thallo- 
phytes, but the leaves of Mosses are simpler in their structure 
than those of higher plants. They often consist of a flat expansion 
composed of a single layer of cells which are all alike, but in a few 
species the cells are in more than one layer and one or two simple 
nerves are developed. The stems, of the higher forms at least, 
have an axial bundle of elongated, thin-walled cells which must be 
regarded as anticipating the fibro-vascular bundles of the higher 
plants, though true vessels are never developed. 

Mosses differ from most of the higher plants in their branching. 
The thalloid forms mostly branch dichotomously, and the branches 
of the foliose forms do not spring from the leaf-axils, but from 
the side of the leaf, or from a point below it. The stems increase 
in length by means of a single terminal cell, and in many cases the 
plants continue to grow at the apex, while dying away at the base. 

The organs of reproduction consist of antheridia and arche- 
gonia. These are sometimes borne solitary on the gametophytic 
stem or thallus, but more commonly in groups; sometimes both 
kinds of organs in the same group, sometimes the different kinds 
in distinct groups. They are often closely associated with hair-like 
bodies, called paraphyses, and are not infrequently surrounded 
with slightly modified leaves, called the pericJiaetiam or the perigy- 
nium. 

The antheridia are short-stalked, multicellular bodies, spherical, 
oblong, ovate or club-shaped in form, and produce in their interior 
cells multitudes of minute, slender, spirally-coiled, biciliated 
sperms. The latter are thicker at one end, and it is to the opposite 
end that the cilia are attached. (See Figs. 581 and 582.) 

The archegonia are flask-shaped, multicellular bodies, with a 
narrow, elongated neck, and a relatively thick, rounded base. 
They possess at first an axial row of cells, the one in the dilated 
base being of larger size than the rest, and constituting the egg 
cell. Later, the axial cells of the neck dissolve into mucilage, 
through which the sperms penetrate to the egg cell. The former 
are discharged from the antheridia when moisture is present, and 



370 



PART IV. — TAXONOMY. 



it is through the medium of the water that they find their way to 
the archegonia. (See Fig. 583.) 

The fertilization thus effected initiates an important series of 
changes resulting in the production of the plant of the asexual 



Fig. 582. 




Fig. 583. 



Fig. 579. — The common Hair-cap Moss, Polytrichum commune, in fruit. 
a, stalked sporogonium covered with a calyptra. 

Fig. 580. — Sporogonium somewhat magnified, and with the calyptra removed, 
showing operculum, a. 

Fig. 581. — Paraphyses and antheridia, one of the latter emitting sperms, a. 

Fig. 582.---Sperms, highly magnified. 

Fig. 583. — Female organ, or archegonium, highly magnified, a, egg cell. 



generation, the sporophyte, very different in appearance from the 
gametophyte, but growing up in contact with it, and technically 
called the sporogonmm. The process of development is as follows : 
The fertilized egg cell, still enclosed within the archegonium, 
divides repeatedly in different directions, and the lower portion of 
the cell-mass thus formed penetrates the tissues of the parent 
plant, and the rest develops outward, stretching and finally rup- 



CHAPTER IX. — THE BRYOPHYTA, OR MOSS PLANTS. 



371 



turing the walls of the archegonium, which, immediately after 
fertilization, usually increases considerably in size, and then stops 
growing, while the sporogonium continues its development. As 
this proceeds, the basal part usually develops into a stalk, some- 
times of considerable length, while the apical portion swells into a 
capsule, which produces in its interior multitudes of minute spores. 
(See Fig. 584.) 

The archegonium, in some species, is ruptured at its apex by 





Pig. 584. 



Fig. 585. 

Fig. 584. — Development of sporogonium of 
Funaria hygrometrica. a. archegonium already 
much stretched by the development of the sporo- 
gonium, s ; the lower part of which has penetrated 
the tissues of the stem, and the upper part of 
which carries the calyptra, c. Magnified about 50 
diameters. After Sachs. 

Fig. 585. — Sporogonium of Phascum muticum 
cut open so as to show the columella, c. to which 
a few spores are still attached. Magnified. 



the growth of the sporogonium, and then its torn remains are seen 
as a kind of sheath at the base of the stalk; in others, and more 
commonly, it ruptures near the base, and then is borne like a 
cap, called the calyptra, at the top of the capsule. (See Fig. 
579, a.) 

The sporogonia, when ripe, differ in structure and mode of 
dehiscence, in ways which are more or less characteristic of the 
genera. In some, there is developed in the interior of the capsule 
an axial organ, called a columella, around which the spores are 
borne (see Fig. 585) ; in others, no such organ is present. In the 
capsules of some, there are developed among the spores peculiar 
filamentous, usually spirally coiled, bodies, called elaters, which 
aid in the ejection of the spores after the capsules are ripe; in 
other species elaters are wanting. 



172 



PART IV. — TAXONOMY 



In some species, the capsule splits, when ripe, longitudinally 
into two or four valves; in others, the dehiscence is transverse and 
the upper part, called the operculum, comes off like a lid; in a few 
forms the dehiscence is irregular, and rarely there is none at all, 
but the spores are set free by the decay of the capsular walls. 

The spores are minute cells with the wall differentiated into 
two parts, a thicker outer coat, called the exospore, and a thinner 
interior one, which is very distensible, like the inner coat of a 
pollen-grain, called the endospore. In germinating, the exospore 
ruptures, and the endospore becomes distended into a tube, which 
usually divides transversely and forms a mass of green, branching 
filaments, which resemble some of the filamentous algae; this is 
the protonema, from which either directly or by production of 
lateral buds, the plant of the sexual generation is developed. (See 
Fig. 586.) 




Fig. 586. — Germinating spores and protonema of Moss, a, a, spores in dif- 
ferent stages of germination ; b, filaments of the protonema ; c, bud on protonema 
destined to develop into a leafy plant. Magnified about 550 diameters. 

The Bryophytes number about 16,000 species and are divided 
into two classes, the Hepaticae or Liverworts and the Musci or 
Mosses. 

THE HEPATIC^, OR LIVERWORTS. 



The Hepaticae, or Liverworts, are the lower in organization. A 
few forms still live in water, thus establishing a connection with 



CHAPTER IX. — THE HEPATIC.-E, OR LIVERWORTS. 373 

their supposedly ancestral forms. The majority are land plants 
but prefer moist or at least shady locations. In some species the 
thalli are lobed and liver-shaped, and in accord with the old-time 
"doctrine of signatures" they were assumed to have medicinal 
value in the treatment of the diseases of the liver — hence the 
name Liverwort. They include many thalloid forms, and the leaf- 
bearing or foliose ones present a simpler structure than the 
Mosses, proper. Their sporogonia, if they dehisce at all, open 
lengthwise, usually into four, but sometimes into two, valves. 
Except in one order, the Anthocerotea?, they do not possess a 
columella. Most of the species are provided with elaters. The 
remains of the archegonium are never borne on the top of the 
sporogonium. 

In habit of growth, nearly all of the species lie prostrate on 
the substratum, presenting one side to the light and having the 
other in shade. The two surfaces accordingly have a different 
structure, rhizoids being usually developed in great numbers on 
the shaded but not on the illuminated side; the latter, in the 
thalloid forms, also often possesses stomata, while the other does 
not. The flattened forms usually branch dichotomously, and in 
some of these there is no indication of leaves, while in others, as in 
the Marchantias, scale-like bodies, doubtless to be regarded as 
imperfectly developed leaves, occur on the under surface. 

In the foliose forms, there are two vertical rows of leaves, very 
simple in their structure, on opposite sides of the stem, and usually 
a third row of less perfectly developed ones on the side next the 
substratum. 

There are about 4,000 species, grouped in four orders, as 
follows : 

The Ricciales are thalloid forms which branch dichotomously, 
and produce their antheridia and archegonia sunken in a groove 
along the middle line of the upper side of the thallus (gameto- 
phyte). The sporophyte is reduced to a globose unstalked sporogo- 
nium which does not bear elaters, and does not spontaneously 
rupture when ripe. It bears many spores. The plants are of 
small size, and not numerous in species. Some of them, as Riccia 
fluitans and R. natans, are not uncommon in fresh water; others, 
as Riccia glauca, grow on damp soil. 

Anthocerotales is a small order of inconspicuous Liverworts, 
of which Anthoceros is representative. The gametophyte is a 
simple, flattened, irregularly-lobed thallus, which is elosely attached 



374 



PART IV. — TAXONOMY. 



by means of rhizoids to the damp soil in which they grow. The 
archegonia and antheridia are imbedded in the upper surface of 
the thallus. After fertilization a sporogonium develops which is 
remarkable in that it is chlorophyll-bearing and thereby able to 
make food for itself, though dependent on the gameophyte for its 
water supply. Accompanying the green tissues are stomata, allow- 
ing of an air-supply, while a columella running lengthwise through 
the sporophyte carries the spore-bearing tissues. The development 
of a root would make this green sporophyte an independent plant 
and to this extent it anticipates the two independent generations 
of some of the Pteridophytes. Anthoceras l&vis, one of the most 
commonly observed species, is illustrated in Fig. 587. 




Fig. 587. — Anthoceros laevis. Portion of thallus showing sporo- 
gonia, s, s, dehiscing into two valves ; c. columella. 



The Marchantiales include the most familiar Liverworts. They 
have thalloid, dichotomously branching stems, producing numerous 
well-developed stomata on the upper surface, and abundant rhi- 
zoids and two rows of small scale-like leaves on the lower. The 
antheridia and archegonia are borne in separate, stalked recep- 
tacles. The spore-capsules dehisce variously in different species, 
sometimes by four valves and sometimes irregularly, and the ejec- 
tion of the spores is aided by spirally ,coiled elaters. 

Marchantia polymorpha is found everywhere on damp ground, 
on wet rocks adjacent to springs and waterfalls, and on the damp 
earth of greenhouses. Fig. 558, A, represents a male plant bearing 
an erect, stalked, wheel-shaped receptacle (gametophore), a, in 
the upper surface of which numerous antheridia are imbedded. 



CHAPTER IX. — THE HEIUTICVE, OR LIVERWORTS. 



37! 



Fig. 558, B, represents a female plant of the same species, bearing 
a female gametophore which consists of a star-shaped body borne 
at the summit of an erect stalk. On its under surface, near the 
base of the rays, when the organ is young, are borne the flask- 
shaped archegonia. 




Fig. 5S8. — Marchantia polymorpha. A, male plant bearing a stalked gameto- 
phore; a, producing antheridia. B, female plant, bearing a stalked gametophore. 
b, from which sporogonia have developed on the under surface of the rays; g. 
one of the receptacles with gemmae; m. one of the gemmae magnified; e, elaters 
highly magnified, and s. a spore clinging to the" elaters. 



The fertilized egg cell develops into a rounded sporogonium, 
containing many spores accompanied by elaters. At the base of 
this stalked sporogonium may be seen the remnants of the arche- 
gonium from which it grew. The spore-capsule bursts to discharge 
the spores, their expulsion being aided by the hygroscopic move- 
ments of the elaters. The spores are dispersed by the wind and, 
upon germinating, produce new thalli. 

Vegetative reproduction is provided for by the development, 
on the thallus, of cups containing gemmsp, (Fig. 588, g) , which have 
the nature of separable buds (Fig. 588, m) and, when washed out 
or blown by the wind, are able to produce new plants. During the 
growth of the thallus the older portions may decay, setting free 
the younger parts and thus giving rise to new plants. 

Since the thallus bears the gametes, it is termed the gameto- 
phyte, while the sporophyte is represented by sporogonium. 

The Jungermanniales constitute the largest order of the Liver- 
worts, numbering aoout 3,000 species. A few of them have thal- 
loid, but the great majority, foliose stems. They produce solitary 
sporogonia which ordinarily split into four valves, from the apex 



376 PART IV. — TAXONOMY. 

downwards, and produce numerous spores and spiral elaters. (See 
Fig. 589.) 

In the foliose forms the leaves occur, as has already been 
described, in three longitudinal rows, and two of the rows are 
conspicuous and spread out laterally, while the third occurs on the 
shaded or under side, and its members are not so well developed. 

The leaves are very delicate, scale-like, destitute of a midrib 
and are of but one cell in thickness. The antheridia are usually 
found among the leaves and the archegonia at the apex of the 
shoots. These may occur on the same plant (monoecious) or on 
different plants (dioecious). Many of the species are common in 
damp soil and on tree trunks. They are plants of wide distribu- 
tion, occurring both in tropical and temperate climates. 

THE MUSCI, OR MOSSES. 

The Musci, or Mosses, are all leafy-stemmed plants, and the 
leaves are all of the same kind and very seldom two-ranked. The 
spores produce a protonemo, of felted, green filaments which may 
increase indefinitely by an apical growth, but sooner or later gives 
rise to lateral buds which develop into' the leafy plant. See Fig. 
586. When the sporogonium develops in the archegonium, the 
latter usually ruptures at the base, and is carried up as a calyptra 
on the top of the capsule. In the great majority of cases the latter 
has a circumscissile dehiscence, and the operculum comes off like 
a lid. The columella is always present, and the capsule never 
produce elaters. Mosses propagate abundantly by vegetative 
processes. Most of their cells are able to develop protonemas. 
Many can provide gemmae. Shoots separated from the parent 
plants give rise to new plants and thus the moss carpets frequent 
in woods and bogs are formed. 

There are three orders of Mosses, as follows: 

The Sphagnales, or Bog-mosses, which grow in tufted masses in 
boggy places, about springs and along the banks of mountain 
brooks, where the supply of water is constant. They are included 
in one genus, Sphagnum; they have in the shade a bright green or 
a pale green, but in exposed locations a red color, straight stems 
growing indefinitely at the ends and producing numerous laterally 
spreading, fascicled branches, which are covered with closely imbri- 
cated leaves. The latter are veinless and consist of a single layer 
of cells, but these are of two kinds, one large, narrowly linear, 
chlorophyll-bearing, and forming a net-work, and the other color- 



CHAPTER IX. — THE MUSCI, OR MOSSES. 



377 



less, perforated by pores and serving to absorb and hold water by 
capillarity, whence the notable water-retaining property of Sphag- 
num. The antheridia are borne on club-shaped or catkin-like 
axillary branches, and the archegonia are commonly in groups of 
three or four enclosed in a bud-like involucre at the ends of the 
upper branches. The spore-capsule is round and operculated, but 
without a peristome, and pedicelled, but the pedicel, known as the 
pseudopodium, instead of being a part of the sporogonium, as is 
usually the case in other Mosses, is a prolongation of the axis of 
the gametophyte. The germination of the spores produces a flat 
thallus, like the Liverwort, and not a filamentous protonema such 
as the higher Mosses possess. One of the Sphagnums is illustrated 
in Fig. 590, A and B, 




Fig. 589. 
-Jungermannia 



bidentata. 



Fig. 590. 

sporogonium dehiscent into four 



Fig. 589. 
valves. 

Fig. 590.— Sphagnum cymbifolium. A, mature plant bearing leafy branches, 
br, and capsules, z. B, one of the capsules, considerably magnified, showing 
operculum ; c, is the remnant of the wall of the archegonium. 



The Sphagnums are the Mosses that form peat-bogs, and these 
are, in some countries, an important source of fuel. By reason of 
its water-holding quality Sphagnum is employed for wrapping and 
packing living plants for shipment. When properly cleaned and 
dried it has been employed as a surgical dressing, for which its 
absorptive power makes it especially useful. 



378 



PART IV. — TAXONOMY. 



The Andraeales. This is a small order of dark colored, branching 
mosses, of rather diminutive size, mostly growing on damp rocks 
in mountainous regions. They produce capsules which have a 
closely adherent, thin calyptra, and a central columella, which is 
free at the apex; they dehisce longitudinally into four or rarely 
six valves. These separate in the middle to shed their spores, but 
remain united both at the base and apex. See Fig. 591. The 
capsules are stalked, but the stalks are formed as in the Sphag- 
nums. 

The Bryales constitute by far the largest as well as the best 





B 



Fig. 591. — Andraea. A, fruiting plant: B. capsule, magnified; C, dehiscent 
capsule and calyptra. 

Fig. 592. — Capsule of Fcmtinalis. one of the Bryales, with calyptra and 
operculum removed, showing the double peristome; a, inner, b, outer peristome. 
Magnified. 

developed order of Mosses. It is one of this order that is illus- 
trated in Figs. 579 to 583, inclusive. They are usually, low, tufted 
plants, with generally cylindrical or rarely slightly compressed or 
somewhat angular, leafy stems, the gametophytes. The leaves are 
simple, and, in some species, composed of but one stratum of cells; 
in others, of more than one; in some, the leaves are nerveless, in 
others there is a single median nerve, and in still others two small 
nerves at the base. 

The reproductive organs are, in most cases, enclosed in a peri- 
dhsetium or perigonium. The sporophyte consists simply of the 
sporogonium or Spore-capsule which is traversed perpendicularly 
by a columella which is attached both above and below; in a very 
few , 3 species the capsule either does not open at all or breaks 
irregularly; in the great majority it dehisces by means of an oper- 



CHAPTER X. — THE PTERIDOPHYTA, OR VASCULAR CRYPTOGAMS. 379 

culum. The orifice thus exposed is sometimes naked, but in most 
cases has a peristome. The latter may either be single or double, 
having one part within the other. The outer peristome consists 
of a row or circle of teeth which, in different species, vary in num- 
ber from four to thirty-two or more. The inner peristome, if 
present, consists of a yellowish pellucid membrane, which is often 
latticed, and attached to the inner base of the outer peristome, and 
is itself segmented or toothed at the top. (See Fig. 592.) 

The spores are dispersed by the wind and upon germinating 
develop into the protonema, already described. From buds on the 
protonema grow stems (gametophores) and at the tips of these 
the antheridia and archegonia are borne. Free-swimming sperms 
of spiral form are given off from the antheridia. Fertilization is 
effected through water, probably raindrops. The archegonium 
opens to receive the sperms and the fertilized oospore develops 
into the new sporogonium. 



CHAPTER X. 
THE PTERIDOPHYTA, OR VASCULAR CRYPTOGAMS. 



THE FILICINE.E. — THE EQUISETINE^. — THE LYCOPODINEJE. 

The Pteridophyta, like the preceding series, consist entirely of 
chlorophyll-bearing plants, which are never either parasitic or 
saprophytic. The word "Pteridophytes" literally means "fern- 
plants," the Ferns being the most numerous as well as the most 
important members of this division. About 3,500 species are 
known. 

The term "Vascular Cryptogams" is applied because here, for 
the first time, we find a distinct development of tubes and sieve 
cells constituting a vascular system and permitting of a growth 
in height far beyond that of the Bryophytes. In many of the 
species, in fact, we find a differentiation of tissues almost as com- 
plete as that found in flowering-plants. Moreover, the plant-body 
develops true roots and well-developed stems and shoots, the latter 
forming, in many species, large and beautiful leaves or fronds. 

In the reproductive process, also, great progress is shown over 



380 PART IV. — TAXONOMY. 

that which occurs in the Mosses. They exhibit, like the Bryo- 
phytes, a distinct alternation of generations, but while in the latter 
group the gametophyte is the more conspicuous and better devel- 
oped, the reverse is the case in the Pteridophytes, the plant 
producing the sexual organs being, even in those species in which 
it is best developed, a mere thallus resembling that of some of the 
lower Hepaticae, and commonly perishing soon after the fertiliza- 
tion of the egg cell has been effected, while the sporophyte devel- 
oped from the latter is conspicuous and highly organized. In 
common with the Bryophytes, the Pteridophytes possess distinctive 
Archegonia, hence these two divisions are sometimes grouped 
together as the Archegoniates. 

The process of reproduction, briefly outlined, is as follows: 
The spore borne by the sporophyte germinates and produces the 
protonema, which through cell-division grows into a tiny flat green 
body, the prothallium, so called because of its resemblance to a 
thallus and because it is temporary in its character, a mere fore- 
runner, so to speak, of the plant which is ultimately produced by it. 

In the Ferns, Equisetums and other species in which it is most 
highly developed, the prothallium consists of a flattened body 
attaching itself to moist soil by means of rhizoids growing from 
the under surface, and is always insignificant in size compared 
with the plant which produced the spore. It is composed of chloro- 
phyll-bearing cells, and may continue its growth for some time 
before bearing fructifying organs. These consist of antheridia 
and archegonia. The archegonia, like those of the Mosses, are 
flask-shaped, cellular structures, having an enlarged basal portion 
which contains the egg-cell or oosphere, and a neck through which 
the fertilizing sperms penetrate. The basal portion is buried in 
the the tissues of the thallus, but the neck is free, projecting above 
the surface. The latter is usually short and composed of four 
longitudinal rows of cells. 

In the interior of the young archegonium, an axial row of three 
cells is formed, the lower constituting the egg cell, the other two 
the neck cells, which later are converted into mucilage, the pres- 
sure of which forces apart the cells composing the wall of the 
neck, forming a passage for the sperms. The mucilage which 
oozes out of the opening seems to have an important influence 
also in directing the free-swimming sperms to their destination. 

The antheridia may be produced on another part of the same 
prothallium, or on a different one. They are usually rounded 



CHAPTER X. — CHARACTERISTICS OF THE TTERIDOPHYTES. 381 

cellular bodies, with walls composed of a single layer of cells, and 
borne on the surface of the prothallus. In the interior a number 
of small rounded cells are produced, each of which contains a 
spirally coiled sperm, provided at its anterior or small end with 
numerous vibratile cilia. Both organs are usually borne on the 
under surface of the prothallus, and the sperms are set free when 
the surface is bathed in water, and through this medium they 
swim about, finding their way ultimately to the mucilage dis- 
charged at the orifice of the archegonium, and pass through it to 
the egg cell. The first sperm to reach the egg cell penetrates it, 
thus completing the act of fertilization, and at once a fertilization 
membrane is formed about the fertilized egg cell, through which 
the remaining sperms are unable to enter. The egg now begins 
to develop in the bottom of the archegonium, and by means of a 
root-like process which it sends into the tissues of the prothallus, 
for a time derives nourishment from the latter, but soon forms 
roots, stems and leaves of its own, and becomes independent. 

In the Mosses, under the same circumstances, only a sporogo- 
nium, which remains attached to the parent plant, and seems a 
part of it, is produced; but here it develops into a conspicuous and 
highly organized plant, usually with an unlimited period of growth, 
and possessing roots, stem and leaves. This plant at maturity 
bears, usually either on the ordinary leaves, or on others specially 
modified for the purpose, a multitude of spores corresponding to 
those produced in the capsules of Mosses. These are borne in 
organs called sporangia, and their structure and the way they are 
borne form a basis for the classification of the members of the 
Fern group. 

Great differences exist in different members of the group, in the 
degree of development which the prothallus attains. In the Ferns, 
and other of the lower members, it is comparatively well developed, 
while in some of the higher forms it tends to disappear entirely, 
being reduced to one, or a very few cells, which do not emerge 
from the coats of the germinating spore. 

While the life cycle in Ferns is nearly always as above 
described, yet in some instances the sporophyte may grow out 
directly from the prothallus without fertilization intervening, a 
phenomenon known as Apogamy, and, conversely, prothallia some- 
times arise directly from the leaves of the Fern plant, without the 
intervention of spores, a condition known as Apospory. 

Some of the species produce but one kind of spores, while 



382 PART IV. TAXONOMY. 

others produce two sets, one of large size, called megasporcs, which, 
in germinating, produce prothallia bearing archegonia only, and a 
smaller, called microspores, whose prothallia produce antheridia 
only. The former species are called homosporous, the latter, 
heterosporous. 

Three classes are usually recognized: The Filicinese, the Eqni- 
sitinese, and the Lycojiodinese. 

THE FILICIN^E, OR FERNS. 

In the Ferns, the sporophyte plants have solid, mostly unbranch- 
ing, or but sparingly branching stems, which, in our species, are 
all subterranean; but in some tropical or sub-tropical forms rise 
above ground and form scaly trunks, sometimes of considerable 
size. They all increase in length by the division of the cells of a 
meristematic region at the tip of the stem. 

The leaves are more highly developed than in any other group 
of vascular cryptogams. They are ample, petioled, sometimes 
stipulate, and commonly, though not always, fork-veined; they 
usually unfold circinately, increase in length by an apical growth, 
and often branch into very compound forms. 

The roots are true roots, in structure and function like those 
of the Seed Plants and not rhizoids such as occur in the gameto- 
phyte. 

The vascular bundles are of the concentric type, and of that 
variety of it which has the xylem tissues located centrally, and 
ensheathed by the phloem. In the stems the bundles are usually 
disposed in a single circle, as has already been explained. (See 
page 224, Part II.) 

The sporangia are always borne on the leaves, either on those 
of the ordinary form, or on those slightly modified for the purpose. 
They are either borne at the margins or on the under surface, 
most commonly in groups or clusters, each called a sorus (plural 
sori). The sporangia are cellular sacs, whose walls consist of a 
single layer of cells, and enclose usually a considerable number of 
spores. 

To the Filicinese belong by far the larger part of the existing 
Pteridophytes. According to the structure of the sporangia the 
class is divided into two sub-classes, the Eusporangiatse., with the 
wall of the sporangium composed of several layers of cells, and 
Leptosporangiatse, with the wall of the sporangium composed of 
but one layer of cells. 



CHAPTER X. — THE FELTCINE^, OR FERNS. 



383 



The first sub-class includes but one order, the Ophioglossales, 
or Adder's Tongue Ferns; the second sub-class includes the Fili- 
cales or Ferns Proper, and the Hydropteridales, or Water Ferns. 




Fig. 593. — Ophioglossum vulgatum. A, entire plant; f, fruiting portion of 
leaf. B, part of fruiting portion of leaf, magnified, s, rounded portion of mar- 
gin, containing in its interior a sporangial cavity, as shown below at sp, where 
a portion lias been cut away so as to show the internal structure. 



384 PART IV. — TAXONOMY. 

The Ophioglossales comprise a small order, the members of 
which consist of a stem, bearing a single leaf, and arising from 
a fleshy root. This leaf bears a fruiting segment on its upper 
side, upon which are developed in a spike or panicle, rows of spor- 
angia formed from the inner tissues of the leaf. See Fig. 593. 
Ophioglossum, or Adder's Tongue Fern, and Botrychium, or Grape 
Fern, are the common genera. The tropical order Marattiales is 
related. 

Filicales. This constitutes by far the largest order and includes 
all the plants we ordinarily call Ferns. They have a wide range 
but reach their highest development in the tropical Tree Ferns. 

The spores in germinating produce at first a filament, one end 
of which soon expands into a flattened tissue consisting of one 
stratum of cells. By further growth it becomes two-lobed or 
cordate at the apex, the growing point being located between the 
lobes, and the middle portion of the prothallus becomes several 
layered. This is the gametophyte and it is usually better developed 
and longer lived than in other vascular cryptogams. It consists of 
a flat, green thallus, attached by one surface to the soil by means 
of numerous simple rhizoids. 

The sexual organs of both sorts are borne on the under surface. 
The antheridia are rounded bodies usually produced in abundance 
at the margin and on the posterior surface of the younger pro- 
thallus along with the rhizoids. In the majority of cases they 
consist of a single layer of cells enclosing mother cells, which, by 
division, form the sperms. The antheridium when ripe absorbs 
water, which causes it to burst at the apex, and the mother cells 
containing the sperms are set free. Soon after, the walls of these 
cells burst, each setting free a sperm which is coiled spirally, and 
provided at its thinnest end with numerous cilia. 

The archegonia are usually borne on the thicker, middle part 
of the older prothallia. They are flask-shaped bodies with necks 
rather short, and curved backward or toward the base of the 
prothallium. See Fig. 594. Usually, the antheridia and arche- 
gonia are not ripe on the same prothallus at the same time and 
cross-fertilization is thus provided for. 

The mode of fertilization and the development of gametophyte 
from the fertilized egg cell are essentially the same in the entire 
class. It has already been described at the beginning of this 
chapter. All the Filicales are homosporous. 

The stems in a few instances, as in Pteris aquilina, have_ the 



CHAPTER X. — THE FILICALES. 



385 



internodes rather long and not covered by the persistent leaf-bases, 
but, in most instances, the nodes are crowded together, and the 
leaf-bases completely obscure the stem, giving it a scaly appear- 
ance. 

The leaves and stems often bear hairs which are usually flat- 



an 





Fig. 594. — A, under surface of prothallus of 
one of the Polypodiaceae, magnified about 25 
diameters, showing three archegonia, a, near the 
heart-shaped apex, and farther back among the 
rhizoids, r, several antheridia, an. 

B, an antheridium, magnified about 125 diam- 
eters, showing cells, c, containing coiled sperms, 
s is the cap-cell, which, when the antheridium is 
ripe, ruptures to free the sperms, p is a portion 
of the prothallium on which the antheridium is borne. 

C, is a ripe archegonium, also magnified about 125 diameters, p, portion of 
prothallium in which the base of the archegonium is imbedded ; g, egg-cell ; n, 
neck of archegonium, consisting of four rows of cells; m, mucilage discharged 
from neck. 

D, sperms, magnified about 500 diameters. 



tened and sometimes conspicuous for their size, forming a brownish 
chaff which, not infrequently, as in the Male Fern, completely 
invests the young leaves. These hairs are technically called paleae. 
The sori, in their arrangement, usually bear a definite relation 
to the venation of the leaves, and as this is different in different 
groups, it affords an important means of distinguishing genera 
and species. For example, in Pteris they are borne on the lower 
margin along the terminations of the veins, and are protected by 
the revolute margins of the leaf; in Hymenophyllum, they occur 
on prolongations of the veins; in Polypodium, they are on the 



386 



PART IV. — TAXONOMY. 



under surface at the extremities of short veins; and in Acrosti- 
chum, they occur anywhere on the lower surface, sometimes cover- 
ing the greater portion of it. 

In some species the sori are naked, that is, not enclosed by a 
protecting membrane or indusium, but in many, such a membrane 
is present, and its form and structure often afford characters by 
which groups are distinguished. In the Shield-ferns, for example, 
the indusium is shield or kidney-shaped; in the Aspleniums it has 
one edge attached to a vein while the other is free; and in some of 
the Cyathaceae it is capsular and completely encloses the sporangia. 

The sporangia themselves differ considerably in different 
groups. In the Polyjwdiaceas, the sub-order to which most of our 
common ferns belong, it has the structure represented in Fig. 
595, B. The upper part, or sporangium proper, has a row of 
thick-walled cells, a, which begins at the upper part of the stalk, 




-*? 



Fig. 595. — Polypodium vulgare. A, rhizome and two leaves, one showing 
the inferior surface and sori; s, is one of the sori. B, a sporangium of one of 
the Polypodiaceae. a, annulus, composed of thick-walled cells extending ver- 
tically around the sporangium to d; near d, the dehiscence begins; s, stalk of 
the sporangium. 



CHAPTER X. — THE FILICAEES. 



*,87 



s, on one side and passes vertically over to the other side, but 
terminates at d before it again reaches the stalk. This row of 
cells is called the annulus, and it is at or near where it terminates 
that the sporangium ruptures when ripe. The dehiscence is trans- 
verse, and the spores are ejected by the elastic straightening of 






Fig. 596. 



Fig. 597. 



Fig. 596. — Salvinia natans. A, portion of plant showing aerial leaves, a; sub- 
merged leaves, b; and sori, s, borne on the submerged leaves. B, a cluster of the 
sori in section, magnified about 10 diameters, n, a sorus containing macrospor- 
angia, and m, m, sori containing microsporangia. Partly after Sachs. 

Fig. 597. — Marsilea salvatrix. st, stem, bearing roots and leaves; 1, leaf 
petiole giving off a fructifying branch ; f, f, fruits, containing sporangia which 
bear both macrospores and microspores. 

the annulus. In this group, as we have seen, the annulus is incom- 
plete, that is, it does not pass completely around the sporangium; 
in the Hymenophyllums and in the Cyathacex, however, it is com- 
plete. In some other species, as in the Osmundas, it is wanting 
entirely. 



388 PART IV. — TAXONOMY. 

Hydropteridales. In this order the spores are of two kinds, 
borne in separate sporangia. Some produce single, large mega- 
spores; others, much smaller microspores in considerable numbers. 
Both kinds of spores produce very rudimentary prothallia (game- 
tophytes) which project but little from the wall of the germinating 
spores. The gametophytes developed from microspores produce 
antheridia only, while those which are developed from megaspores 
produce archegonia only. 

The order is a small one, consisting of two sub-orders, the 
Salviniacese and the Marsiliacex, each represented by but a few 
species. The Salvinias are aquatic in habit; the Marsilias grow in 
marshy places. See Figs. 596 and 597. 

THE EQUISETINE^E, OR HORSETAILS. 

The plants of this class are readily distinguished by their 
hollow, cylindrical, jointed and fluted stems, their sheath-like 
whorls of united leaves, and their terminal, cone-like fructifications. 
The internodes of the stem are hollow, but each node is closed by 
a membrane; the leaf-sheath is broken up into a number of points 
at its apex, each point corresponding to the tip of a leaf, and for 
each there is a corresponding fibro-vascular bundle, which at the 
base of the sheath passes into the stem, thence straight down it 
to the node next below, where it forks into two, the branches 
coalescing with those of the stem. 

The stems are all herbaceous and mostly perennial, from creep- 
ing, underground stems or rhizomes; the aerial branches are of two 
kinds, fertile and sterile, and are usually started. at the close of 
the season, persist over winter and are ready for growth the fol- 
lowing spring. The stems are sometimes simple; sometimes they 
are branching, and the branches, which have their origin on the 
inside of the base of the leaf-sheath, are arranged in whorls. The 
stems grow from a terminal, triangular-pyramidal cell. 

The fertile branch containing the fruiting cone usually appears 
first in the spring and commonly bears no side branches or foliage 
leaves. The cone or strobilus consists of compactly arranged whorls 
of sporangiophores, each of which is a flattish, usually hexagonal 
shield, elevated centrally on a short stalk, and bearing around its 
interior margin the sporangia, usually from five to ten for each 
shield. The spores produced in the latter are provided with elaters, 
which being hygroscopic, coil and uncoil as the amount of moisture 



CHAPTER X. — THE EQUISETE/E, OR HORSETAILS. 



!8<) 



present increases or diminishes, the movements aiding the ejection 
of the spores from the sporangia. See Figs. 598 and 599. 

All the existing species of Equisetums are homosporous, though 
some of the fossil members of the class, represented in their fossils 
in coal and in rock, were heterosporous. Most of the living forms 
are practically dioecious, some of the spores producing male and 
others female gametophytes. This, however, is probably not due 
to any inherent difference in the spores but to difference of nutri- 
tion, the gametophytes which are well nourished producing arche- 
gonia only or mainly, while those which receive a deficient supply 
of nutriment bear antheridia only. 







Fig. 599. 



Fig. 598. — Portion of Equi- 
setum sylvaticum, showing 
fruiting cone, a, at the apex 
of the stem ; b, transverse 
section of stem somewhat 
magnified. 

Fig. 599. — Equisetum syl- 
vaticum. a, fruiting scale, 
magnified, showing sporan- 
gia : b. one of the spores 
enveloped in the elaters ; c, 
one of the spores with elaters 
extended. 

Fig. 600. — Fruiting plant 
of Equisetum arvense; a, 
strobilus ; b. transverse sec- 
tion of stem, showing hol- 
low and circle of fibro-vas- 
cular bundles and large in- 
tercellular spaces. 




Fig. 598. 



Fig. 600. 



The forms of the prothallia in the Equisetums are usually more 
irregular than those of Ferns, commonly developing lobes or 
processes of various sizes. The antheridia are apically or margin- 
ally situated, and the archegonia, though first formed on the mar- 



390 



PART IV. — TAXONOMY. 



gin, on account of the continued growth of the gametophytes, come 
to occupy the upper surface. The sperms are of much larger size 
than those of the Ferns. In other respects, the mode of sexual 
reproduction in these plants closely resembles that of the Ferns. 
Fig. 600 represents a fruiting plant of Equisetum arvense, a 
species common in damp, sandy soil, and which produces from its 
rhizomes chlorophylless, simple stems that mature their spores 
early in the spring and then die, and later develop freely branching 
green stems that continue to grow during the season. Figs. 601 
and 602 show, respectively, male and female prothallia of this 




Fig. 601. 



Fig. 602. 



Fig. 601. — Male prothallus of Equisetum arvense; r, rhizoid ; a, a, a, anther- 
idia in various stages of development. Magnified about 300 diameters. 

Fig. 602. — Part of female prothallus of Equisetum arvense. a, a, archegonia ; 
b, branch of prothallium ; r. one of the rhizoids. Magnified about 300 diameters. 



plant. Both are so small that a lens is needed to identify them. 
Rather seldom do they survive in our climate and our species of 
Equisetum are chiefly propagated vegetatively. 

The forms of Equisetinese, at present in existence, are all 
included under the one genus, Equisetum, and this does not contain 
a large number of species; the individuals, however, are abundant 
and widely distributed. Certain species are abundant along raii- 



CHAPTER. X. — THE LYCOPODINE^E, OK CLUB MOSSES. 391 

road embankments and exposed locations, while others are found 
only in moist or shaded places. In temperate climates they range 
in height from several inches to a few feet, but one tropical species 
reaches a height of forty feet. Fossil forms from the carboniferous 
period are abundant, some attaining the size of trees. Some of the 
species known as Scouring Rushes are remarkable for the large 
amount of silica contained in the epidermis. 

THE LYCOPODINE.E, OR CLUB MOSSES. 

The plants of this class are, for the most part, small or moder- 
ate sized perennial herbs, sometimes with stems erect and rooting 
at the base, but more commonly creeping, with ascending or erect 
branches, which, in the majority of cases, originate dichotomously, 
though in some instances monopodially. With few exceptions, the 
stems and branches are thickly clothed with leaves. The latter, 
in the simplicity of their structure, are in strong contrast to those 
of the Ferns, being mostly of small size, without petioles or 
stipules, usually provided with but a single vein, which constitutes 
a mid-rib, and the blade is never branching or compound. 

The sporangia are, in the majority of cases, borne on the leaves, 
but, in some instances, as in Psilotum and Selaginella, on the stem. 
The spore-bearing leaves may be of the ordinary form, or they may 
be somewhat modified in structure and crowded together, forming 
spikes or cones (strobili) at the ends of some of the branches. Some 
members of the group are homosporous, others are heterosporous. 

There are two orders, the Lycopodiales and the Selaginellales. 

The Lycopodiales, or Club Mosses Proper, include several hun- 
dred species, ranging from the tropics to the -frigid zone. Only four 
genera are known, two of them Australian. All the existing forms 
of the group are homosporous, but the Lepidodendrons of the Coal 
Age, which must be regarded as belonging here, were heterosporous. 
The prothallia are mostly subterranean, tuber-like bodies, which 
bear both antheridia and archegonia. 

The ordinary or spore-bearing plants are all terrestrial, and 
moss-like in appearance, the stems being thickly clothed with small 
simple and often narrow leaves. The stems branch in a dichotomous 
manner by a division of the terminal bud. In habit, the stems may 
either be creeping, with erect or ascending branches, as in Lycopo- 
dium clavatum, or, less commonly, erect from the first, as in Lyco- 
podium Selago. 



92 



PART IV. — TAXONOMY. 



The internal structure of the stems is somewhat peculiar. There 
is a stele or central cylinder containing a large bundle consisting 
of several strands of xylem, with phloem intermingled and a sur- 
rounding sheath. 

In the principal genus, Lycopodium, the sporangia, which are 
one- to three-celled, occur singly in the axils or on the upper surface 
of leaves (sporophylls). See Fig. 603. 




Fig. 603. — Fruiting branches of Lycopodium clavatum, about one-half nat- 
ural size, a, fruiting cone ; b, one of the scales of a cone, showing inner surface, 
and one of the sporangia near its base, considerably magnified ; c, three spores 
highly magnified. 



The sporangia open in a slit-like fashion and shed their spores 
which are distributed by the wind. These spores are very light 
and are very inflammable. They are sometimes used in fireworks 



CHAPTER X. — THE SELAGINELLALES. 



393 



and are known as "vegetable sulphur." They are also employed as 
a dusting powder for infants and in pharmaceutical practise as an 
absorbent coating for pills. 




Fig. 604. — Psilotum triquetrum. A. part of plant, natural size. 15. portion 
of stem, magnified, showing fructifying branch bearing at its apex two sporangia 
between two small leaves. 



Psilotum, a tropical epiphyte belonging to a related family, is 
illustrated in Fig. 604. 

The Selaginellales include two genera, Selaginella and Isoetes. 

The Selaginellas, or Little Club Mosses, are widely distributed in 
nature and are often grown in greenhouses for their decorative 
effect. In general appearance the sporophytes are delicate plants 
and bear a considerable resemblance to the species of Lycopodium, 
but the dichotomous branching is in one plane and not in all planes ; 
the leaves are arranged in four vertical rows, and the members 
of opposite pairs are dissimilar in size or shape; the roots fork 
repeatedly, and the secondary branches decussate with the primary, 



394 



PART IV. — TAXONOMY. 



the tertiary with the secondary, and so on. The sporangia are 
borne on the stem immediately above the insertion of the leaves so 
as to appear in their axils. The sporangia occur singly and are of 
large size compared with those of Ferns; the megasporangia each 
contain four spores, while the microsporangia, which are ordinarily 
borne higher up on the axis, contain numerous microspores. 

Both kinds of spores begin to germinate while yet in the spor- 
angia. The microspore grows into the male gametophyte, consisting 
of a single vegetative cell which bears a simple antheridium. The 
antheridium contains a few, free-swimming, biciliate sperms which 
escape through a fissure in the wall of the microspore. 

The megaspores are several times larger than the microspores 






Fig. 605. — Fruiting branches of Selaginella, about natural size. a, spore- 
bearing portion ; b, sporangium containing microspores, from the inner surface of 
one of the scales ; c, sporangium from the inner surface of another scale, containing 
megaspores. 



and each grows into a multicellular prothallus which protrudes 
through the ruptured spore wall and develops archegonia on the 
outermost part. In some species, fertilization occurs while the 
spores are still on the plants. The fertilized egg-cell grows to an 
embryo having a suspensor and remains for some time imbedded 
in the prothallus. The development of a suspensor is an important 
distinction from the True Ferns and marks an advance toward the 
Seed Plants. Unlike the embryo of the Seed Plants, however, that 



CHAPTER X. — THE ISOETES, OR QUILLWORTS. 



395 



of Selaginella does not go into a resting period, but continues to 
grow until it protrudes its root and shoot from the prothallus and 
finally becomes an independent green plant — the sporophyte. Fig. 
605 represents a portion of a fructifying stem of a Selaginella with 
a microsporangium and a megasporangium enlarged. 

The Isoetes, or Quillworts. In these species the stem is short, 
and the numerous leaves with which it is clothed are long and 
grass-like, and on the upper surface of the sheathing bases occurs 
a depression or pit in which the sporangia are borne, and just above 
this is the ligule. The megasporangia contain numerous megaspores, 
and are borne mostly by the outer leaves of the fascicle, while the 




Fig. 606. — Isoetes setacea. A, the entire plant. B, the base of one of the 
leaves, showing immature sporangium and, above it, the ligule. 



microsporangia are borne on the interior ones. Among the spores 
in both kinds of sporangia are borne cellular filaments or para- 
physes. A few of the species are terrestrial or amphibious in their 
habits, but most are submerged aquatics, growing in water which 
does not contain much calcareous matter in solution. See Fig. 606. 



396 PART IV. — TAXONOMY. 

CHAPTER XI. 
THE SPERMATOPHYTA, OR SEED PLANTS. 



CHARACTERISTICS.— THE GYMNOSPERM^. 

The Spermatophytes or Seed-Plants are characterized by the 
production of seeds. The group contains the largest and most 
highly developed of all vegetable forms; by far the larger propor- 
tion of those plants we most admire for their beauty or desire for 
their usefulness. From them chiefly do we form our conceptions of 
vegetable life. They do more than any others, or all others com- 
bined, to give to the landscape its character and charm. 

We have already discussed the gross structure of these plants 
in Part I and their cellular structure in Part II, gaining thereby 
some idea of the immense variety of shapes, sizes and habits that 
occur among them. Some species, as the Wolffia, are mere green 
specks, barely distinctly visible to the naked eye, while others, as the 
giant Sequoia, attain the lofty height of more than three hundred 
feet. Some pass through the complete round of their life-history 
in a few days, while others outlive many generations of men; some 
have a soft, flabby structure, and are easily destroyed, while others 
are composed chiefly of hard and enduring tissues ; some make their 
homes in the water, others in marshy places, others on dry ground, 
while still others prefer the arid wastes of the desert; some are 
parasitic or saprophytic, but the great majority are chlorophyll- 
bearing; some like the shade, others prefer the open sunshine; some 
flourish only on the borders of eternal snows, while others cannot 
thrive except in the perpetual warmth of the tropics; and there 
are indeed few corners of the earth so inhospitable as not to afford 
some of them a congenial abiding-place. 

While it is probably true that, merely in the number of indi- 
viduals, they are surpassed by some of the Thallophytes, in the 
number of species, approximately 133,000, they probably exceed all 
the other groups of plants put together. 

The term Spermatophytes, or Seed-plants, is appropriately 
applied to the members of the group, because their most distinctive 
characteristic is the production of seeds. These, as we have 



CHAPTER XI. — THE SPERMATOPHYTES, OR SEED PLANTS. 397 

already seen, arc quite complex in their structure, containing within 
their seed-coats an embryo which is usually so far developed as to 
possess the rudiments of stem, root and leaves. They often con- 
tain also an endosperm or perisperm, whose service is to nourish the 
growing embryo. 

Since none of the lower plants produce seeds, there would seem, 
at first thought, to be a sharp line of separation between Seed-plants 
and all others, but such is not really the case. The process of seed- 
production is closely related to the sexual processes in the higher 
Pteridophytes, and the progress from the lowest forms of the latter 
group to the highest forms of Seed-plants, is one of easy gradations. 

In both groups the familiar and conspicuous plant is the sporo- 
phyte; the reproductive organs are, with a few exceptions, borne 
upon modified leaves (sporophylls). In the Seed-plants, however, 
particularly in the higher forms, these leaves, and often also others 
indirectly concerned in the reproductive process, are much more 
strongly modified and form a more or less conspicuous group, which 
we have already studied as the flower. Moreover, the ovules and 
pollen-sacs of seed-plants are homologous respectively with the 
megasporangia and microsporangia of the higher Pteridophytes; 
the embryo-sac in the ovule corresponds with the megaspore, and the 
pollen-grain with the microspore. 

In the lower Pteridophytes, such as Ferns and Equisetums, we 
find that the prothallus or gametophyte generation attains a very 
considerable development, and continues for some time as an inde- 
pendent plant, but in the higher members of the group, as Salvinia, 
Selaginella, etc., it becomes progressively of less and less impor- 
tance, in some cases scarcely emerging from the coats of the 
spore. In Seed-plants the gametophyte is still represented, but its 
degradation is carried a step farther. The female prothallus or 
gametophyte consists of a few cells or a tissue formed in the 
megaspore or embryo-sac, and it never bursts through the walls 
of the latter, but either remains as a part of the seed, or is after- 
wards absorbed by the forming embryo. The seed is, in fact, a 
megasporangium containing a megaspore which, while still in con- 
tact with the parent plant and nourished by it, has germinated 
and produced an internal prothallus or gametophyte (embryo-sac) 
containing an egg cell, and which, after fertilization, has developed 
into an embryo (sporophyte) ; and, only after these processes have 
been accomplished, has it become free. 

In like manner, the pollen-grains are microspores, somewhat 



398 PART IV. — TAXONOMY. 

modified in accordance with the changes in the development of the 
megaspore. They are formed in the pollen-sac in the same way 
that microspores are in microsporangia, but the male prothallus 
which they produce in germinating, is, if possible, still more rudi- 
mentary, and motile sperms are seldom produced. Instead, the 
entire pollen-grain, as we have found, is conveyed by the wind, by 
insects, or by some other agency either to the ovules direct, as in 
the Pines and their relatives, or to the stigma, which is a portion 
of a carpel leaf or whorl of carpel leaves enclosing the ovules, as in 
the higher flowering-plants, and it there germinates and forms a 
pollen-tube which penetrates to the ovule, and through the micro- 
pyle of the latter to the embryo-sac, as was explained in Part I. 

Compared with the Pteridophytes, the various organs of vege- 
tation are more complex and better developed, the modifications of 
form and structure which organs of the same name assume — the 
multiform adaptations of stems, leaves and roots, for example, to 
a variety of uses and changes of form to correspond with changed 
functions — is especially remarkable. 

We have now noted two advances made by the Spermatophytes 
over the preceding groups, both being directly concerned with 
propagation and of great importance. One of these is the distribu- 
tion of the microspores (pollen grains) by the wind or by insects, 
thereby rendering the presence of water unnecessary to fertiliza- 
tion, whereas, in the lower plants, the free-swimming sperms 
require water to enable them to reach the egg-cells. The second 
advance is the formation of the embryonic plant, protected by the 
seed coats and remaining in a resting stage for a considerable 
period, during which the distribution of the seed occurs. Owing to 
these and other advantages, the spermatophytes have spread over 
the earth and have competed successfully with — and often replaced 
— their less fortunate neighbors, the fern and mosses. 

The Spermatophyta is subdivided into two classes, the Gymno- 
spermse in which the seeds are not enclosed by sporophylls (car- 
pels), and the Angiospermas, in which the seed are enclosed in an 
ovary consisting of a single carpel or a whorl of carpels. 

By far the larger proportion of all Seed-plants are chlorophyll- 
bearing. Only a few have developed parasitic or saprophytic 
habits. 

THE GYMNOSPERM^:, OR GYMNOSPERMS. 

The plants of this class are, without exception, woody-stemmed, 
terrestrial and chlorophyll-bearing forms, most of them attaining 



CHAPTER XI. — THE GYMNOSPERMiE, OR GYMNOSPERMS. 399 

a considerable size, and some of them forming the largest of our 
forest trees. In the structure of their stems they show affinities 
with the highest forms of the Spermatophytes, the Dicotyledons, 
since they possess a pith, medullary rays and a cambium; but their 
tissues are less complex, true wood-cells and ducts being largely 
replaced by an intermediate tissue, the discigerous tracheids. In 
many other points they show themselves decidedly inferior to the 
rest of the Spermatophytes, and, in some important respects, 
closely allied to the Pteridophytes. The strobili or flowers, as a 
rule, are of very simple structure, consisting of sporophylls much 
less modified from the ordinary form than in most other flowering- 
plants; they are never showy or nectar-bearing; the stamens and 
pistils are never found together in the same flower, but all the 
plants of the Class are either monoecious or dioecious. As implied in 
the word, gymnospermx, the ovules are not enclosed in an ovary, 
but are borne on the base of an open carpel, or, more rarely, 
naked, on the end of a branch, and the cotyledons of the embryo 
are arranged in whorls, sometimes of two, but often of four, six, 
or some higher number. 

Their alliance to the higher members of the preceding group, 
the heterosporous Ferns, is especially shown in the fact, that a 
female prothallus is produced in the megaspore (embryo-sac) 
previous to fertilization, and bears simple and much-reduced 
archegonia, and in the fact that the pollen-grain develops a vegeta- 
tive cell which grows out as a pollen-tube, and an antheridial 
mother-cell which forms two sperm cells. This structure behaves 
like, and is really the equivalent of, the rudimentary male gameto- 
phyte of Salvinia and Selaginella. 

In descent, the Gymnosperms are an older group than the 
Angiosperms; many fossil species have been determined; their 
sexual generation indicates a closer relationship with the Ferns; 
probably an extinct group of the latter known as Seed Ferns 
(Pteridosperms) were their ancestors. 

The Gymnosperms include three orders, which, in appearance 
and habits of growth, differ widely from each other, but agree 
essentially in their modes of reproduction. They are the Cyca- 
dales, the Coniferales and the Gnetales. 

The Cycadales. The plants of this order have much the aspect 
of Tree-ferns, with which, in fact, they are more strongly allied 
than are any other members of their class, having unbranching 
scaly stems crowned at their summit with ample pinnate leaves. 



400 PART IV. — TAXONOMY. 

They are slow-growing plants which, though once exceedingly 
abundant and playing an important part in the world's flora, are 
now rare, consisting of only about eighty species, and these con- 
fined to tropical and sub-tropical regions. 

The stems, though externally scaly and unbranching, like those 
of Tree-ferns, more closely resemble in their internal structure 
those of the Pines and Dicotyledons, having the woody elements 
arranged in much the same way and growing in substantially the 
same manner. Compared with the Pines the medullary rays are 
broader, and the cells composing them thinner-walled and the pith 
is usually large. The woody elements consist of discigerous, 
scalariform or reticulate tracheids in the secondary wood, with a 
few spiral tracheids in the primary wood or medullary sheath, 
but true tubes are seldom found. The stems also differ from those 
of Ferns, in being continued downward into a tap-root. 

The leaves are arranged on the stem in compact spirals, and 
consist of two kinds, the ample pinnate ones already mentioned, 
and more numerous, scale-like, brown, leathery, rudimentary ones. 
Every year or two the crown of foliage leaves is renewed by the 
unfolding of the large terminal bud. 

The species are all dioecious, the male and female flowers being 
borne on different individuals. Both kinds are borne at the apex 
of the stem, the staminate ones consisting of leaves modified into 
shield-shaped scales compactly arranged on a terminal cone, some- 
times a foot or more in length. Each scale bears on its under 
surface numerous pollen-sacs or microsporangia, which are usually 
collected into groups of from two to five each. See Fig. 607, B. 

The female flower is also, except in the genus Cycas, spike-like 
or cone-like in appearance, the cones often being of large size and 
made up of peltate scales, on the under surface of each of which 
two ovules or megasporangia are borne. See Fig. 607, C. 

The female flowers of the species of Cycas differ from those of 
other members of the order, in the fact that the ovule-bearing 
leaves (megasporophylls) form N a rosette, composed of parts sim- 
ilar in shape but smaller in size than the ordinary foliage leaves, 
and the ovules take the place of the ordinary pinnae. See Fig. 
607, A. Moreover, the axis that bears the floral leaves does not 
stop growing, but is continued upward through the flower and 
bears above the latter both scale-like and ordinary leaves. 

The ovules are orthotropous, and each consists of a nucellus 



CHAPTER XL — THE CYCADALES. 



401 



enclosed in a single thick coat which, at maturity, becomes succu- 
lent. They are of large size, the largest in the vegetable kingdom, 
attaining, in some species, the size of a filbert, before fertilization. 
The young megasporangium (ovule) contains four megaspores 
but only one develops and it remains within the ovule and is nour- 




Fig. 607. — A, carpellary leaf (megasporophyll) of Cycas revoluta, about one- 
fourth natural size, a, one of the pinnae of the leaf; o, o, ovules (megaspor- 
angia) developed in the place of pinnae. B, one of the anther-bearing scales 
(microsporophylls) from a staminate cone of Zamia, one of the Cycads ; p, pollen- 
sacs. C, one of the carpellary scales from the fertile cone of Zamia, showing two 
ovules, ov, ov, pendant from the under surface. 



ished by the tissues of the nucellus. Several archegonia are 
formed at the apical end, imbedded in the tissues of the prothallus 
(endosperm). 

The pollen is wind-borne and upon reaching the ovules pene- 
trates the micropyle and enters a chamber between the micropyle 
and nucellus which is filled with a watery liquid secreted by the 
tissues. Here the pollen grain develops a short pollen-tube which, 
upon rupturing, liberates two very large sperms provided with 
cilia and thus free-swimming. These pass through the open end 
of the nucellus and fertilize the large egg-cell. Several months 
may elapse between pollination and fertilization in this species. 

The Cycads and the related Ginkgo afford the only instance, 



402 PART IV. — TAXONOMY. 

among Spermatophytes, of free-swimming sperms — a fact pointing 
strikingly to their connection with the Ferns. 

Other points of resemblance between Cycads and Ferns are the 
coiled (circinate) vernation of the pinnse, the forked venation of 
the leaves and the presence of fruiting organs resembling sori 
rather than flowers. Although forming a true seed, the embryo 
grows at once into a plant (sporophyte) without an intervening 
resting period such as ordinarily characterizes seeds. 

Cycas revoluta, known sometimes as Sago Palm, is commonly 
cultivated in hot-houses, and another cycad, Zamia integrifolia, 
commonly called the Coontie, is native to the United States, grow- 
ing in southern Florida. 

The Coniferales or Conifers constitute by far the largest and 
most important order of the class. It includes the Pines, Yews, 
Cypresses, Firs, Larches, Junipers, Araucarias, etc. A few of the 
species are shrubs, but most are trees of medium or large size; the 
stems are very commonly excurrent or spire-shaped; branching 
occurs freely, and the branches spring from the leaf-axils, but not 
all, or even the larger proportion of the axils, produce buds; the 
leaves are, with few exceptions, entire, simple-veined and of small 
size, and are commonly very abundant, in some instances, as in 
the Arbor Vitse and Red Cedar, so thickly clothing the branches 
that the branch itself is completely obscured. 

The foliage leaves are usually evergreen, remaining on the 
plant for an indefinite period — ranging from two to ten years. 
Many of the species produce, besides the foliage leaves, brown 
scales, which mainly serve a protective purpose, as bud-scales, etc., 
as in the Spruces; but in one Australian genus, Phyllocladus, no 
green leaves are developed, but leaf-like branches springing from 
the axils of scales, take their place. 

In their internal structure and mode of growth, the stems very 
closely resemble those of Dicotyledons, the most important differ- 
ence being the fact that the elements of the secondary wood consist 
almost entirely of discigerous tracheids. (See Fig. 431, Part II.) 
The larger part of our supply of soft wood timber comes from the 
coniferous trees, especially the Pines. 

Nearly all the species produce terebinthinous secretions, and 
many valuable resinous and oleo-resinous products are obtained 
from the order. 

The flowers are, in some species, monoecious, in others dioecious. 
The staminate flowers consist of shield-shaped scales compactly 



CHAPTER XI. — THE CONIFERALES, OR CONIFERS. 



tu: 



arranged along a lengthened axis, forming a strobilus or cone, and 
each scale bearing on its inferior surface two or more pollen-sacs. 
These often vary in number on the same plant. In the species of 
Spruce and Pine, there are two placed side by side on the staminal 
leaf, very much as in most of the higher flowering-plants; in the 
common Juniper there are three roundish pollen-sacs; in Taxus 
baccata (see Fig. 608, C) there are from three to eight, and in the 




Fig. 608. — The Yew, Taxus baccata, showing flowers and fruit. A, branch, 
with ripe fruit, f, about natural size. B, longitudinal section of female flower, 
showing terminal ovule ; n, nucellus ; c, coat of ovule : a, rudiment of aril, which 
later grows up and envelops the seed ; b, a bract. Magnified about 20 diameters. 
C, male flower, showing terminal cone of staminate, shield-shaped scales, each 
with several pollen-sacs on the inferior surface; a, one of the pollen-sacs. 
Magnified. 



Araucarias of the southern hemisphere, there are a large number 
of long cylindrical ones pendent from the lower surface of the 
shield-shaped scales. The staminal scales are nearly always 
smaller and of a different color from the ordinary ones, but they 
are arranged in a similar manner on the stem. In this respect they 



404 PART IV. — TAXONOMY. 

show their inferiority to Angiosperms, for in the latter the differ- 
entiation between floral and ordinary leaves often extends to the 
phyllotaxy, the arrangement of the floral leaves frequently being 
quite different from that of the foliage leaves on the same plant. 

The ovulate flowers vary a good deal in the different species, 
particularly in the position of the ovules. In some, as the Yews, 
family Taxacese, Fig. 608, B, the flower consists of a naked ovule 
borne at the apex of a short branch; in others, as the Spruces, 
Pines, Larches and Cedars, family Pinacese, they form cones (stro- 
bili) consisting of an axis, along which lateral scales or bracts 
are compactly arranged in spiral order, and in the axil of each 
bract, and attached to it only at the base, occurs another carpellary 
scale, which bears on its upper surface two ovules, whose micro- 
pyles point downward (see Fig. 609, A) ; the Araucarias of the 
Southern hemisphere have flowers of similar structure, except that 
the carpellary scale is completely fused with the bract, in whose 
axil it is borne; in the Taxodiums, represented by the Bald Cypress 
of our Southern States, the fusion between carpellary scale and 
subtending bract, has also taken place, but the micropyle of the 
ovule is directed upward instead of downward; and in the sub- 
family Cupressinex, to which belong the Juniper, Savin, Red Cedar 
and Arbor Vitse, the carpellary scale is completely fused with the 
bract, the micropyle of the ovule is directed upward, and the bracts 
are arranged on the axis in whorls instead of spirals. 

For illustrating more particularly the mode of reproduction in 
this group, we may take the Scotch Fir, Pinus sylvestris. This 
species is monoecious, and the staminate flowers are borne in 
clusters on the lower parts of shoots of the same season. Each 
scale produces two pollen-sacs placed longitudinally, side by side, 
on the lower surface. The pollen-grains are formed early in May 
and when ripe consist of a central body with two vesicular, wing- 
like air sacs, as is frequently the case with the pollen of Conifers. 
The pollen-grain (microspore) upon germination divides into four 
cells, two constituting the prothallus, a third the pollen-tube and 
the fourth the antheridium mother-cell; usually one of the pro- 
thallial cells soon disappears, however, and the mature pollen-grain 
contains but one. 

The ovulate flower is a cone, borne at the apex of a small 
branch. Each fertile scale bears on either side of a central rib, 
near its base, two ovules, whose micropyles point obliquely down- 
ward. The ovule-bearing scale is in the axil of a bract, and 



CHAPTER XI. THE CONIFERALES, OR CONIFERS. 



405 



slightly attached to it at the base. Each ovule consists of a 
nucellus enclosed in a single coat, as is most commonly the case in 
Gymnosperms. Although four megaspores are originally formed 
in the ovule, only the basal one develops, and the others are dis- 
organized and used by it as food. 




Fig. 609. — Pinus sylvestris. A, female cone somewhat enlarged; B, one of 
the fruiting scales considerably magnified, showing upper surface and two ovules 
near its base, pointing obliquely downward. The bract, in the axil of which 
the fruiting-scale is borne, is concealed behind the latter. C, diagram of upper 
part of ovule much magnified ; a, coat of ovule ; m, micropyle ; p, pollen-grain 
sending tube into nucellus, n ; b, embryo-sac filled with endosperm ; c, one of the 
two archegonia. D, scale with ripened seeds ; these each possess a prominent 
wing. E, seed with wing removed and cut longitudinally to show albumen and 
embryo. 



When the ripened pollen-sacs begin to open to shed their pollen, 
the axis of the fertile cone lengthens so as to separate the scales 
and permit the access of the pollen. The latter, conveyed by the 
wind and falling upon" the ovule-bearing scale, slips down it to the 
base, being guided in its course partly by the projecting mid-rib, 
partly by the peculiar formation of the scale, and partly by the 
appendages of the pollen-grains, until they rest in the micropyles 
of the ovules. The pollination thus accomplished, the scales of the 
cone close together at the top, and become agglutinated with 
resinous matter. At the time this takes place the ovule is very 
imperfectly developed, and in this species the process of fertiliza- 



406 



PART IV. TAXONOMY. 



tion occupies a long time, not being completed, in fact, until the 
succeeding year. 

When the ovule is fully matured and ready to receive the fer- 
tilizing influence of the pollen-tube, a large embryo-sac has been 
formed in the nucellus, and this has been filled with cells constitut- 
ing a prothallus (gametophyte), and in this are formed one or 
more archegonia, which structurally resemble the corresponding 
organs of the Pteridophytes, possessing a body, which contains an 
egg-cell, and a neck composed of rows of small cells. The pollen- 
tube, formed from the germinating pollen-grain, penetrates the 
tissues of the nucellus and grows down through them to the neck of 
the archegonium, and its sperm nucleus unites with the nucleus of 
the egg-cell. The fertilized egg-cell then begins to develop three 




Fig. 610. — Pinus sylvestris. A, branch, showing cluster of staminate cones 
near its apex ; a, one of the staminal leaves magnified, showing two pollen-sacs ; 
b, a pollen-grain highly magnified, showing outer coat with two cellular, wing- 
like appendages. The body of the grain contains two cells, one large and one 
small one. 



structures, known as the pro-embryo, the suspensor and the 
embryo-sporophyte. A part of the prothallus is used in nourishing 
the embryo but more is stored as endosperm around it. The time 
of pollination to the ripening of the seed, comprises, in this and 



CHAPTER XI. — THE GNETALES, OR JOINT FIRS. 



40' 



many other species of the Conifers, two entire seasons. The 
embryo, as in many other species of Pinacese and in some other 
Conifers, is polycotyledonous. The reproduction of Pinus sylvestris 
is illustrated in Figs. 609 and 610. 

The Gnetales, or Joint Firs, constitute a small but diversified 
order of plants, consisting of undershrubs, shrubs, and small or 
moderate-sized trees. There are only about forty species in all, 




Fig. 611. — Welwitschia mirabilis, entire plant, about one-thirtieth natural 
ze. After Hooker. 



and these are distributed into the three genera, Ephedra, Gnetum 
and Welwitschia, comprised in the family Gnetacese. The Ephe- 
dras are shrubs or undershrubs with much the aspect of Equise- 
tums, having slender, cylindrical, jointed branches covered with 
a green rind, and bearing at the joints a pair of opposite small 
leaves, which are connate at the base, forming a two-toothed 
sheath. 

The Gnetums also have opposite leaves, but these are large, 
broadly lanceolate or oval, entire, and pinnately veined. The 
remarkable genus, Welwitschia, is represented by but one species, 
Wehvitschia mirabilis, a native of South Africa. It has a short, 
thick stem, which rises but 'a few inches above the soil, and is 
continued downward into a long tap-root. From opposite sides, 
just below the summit of the stem, arise two long, strap-shaped 
persistent foliage leaves, several feet long, and usually more or 
less fringed and torn at the apex, the only leaves the plant 
possesses, and from the circumference of the broad apex of the 



408 PART IV. — TAXONOMY. 

stem, just above these, spring the branches of the cymose inflor- 
escence. These arise from the axils of bracts, and are jointed and 
dichotomously branching. See Fig. 611. 

The flowers in some species of the Gnetacese are monoecious, 
in others dioecious, and both male and female flowers are invested 
and protected by modified leaves, forming a kind of perianth some- 
what similar in character to that of the higher flowering-plants. 
Each stamen bears either two or four pollen-sacs, the ovules, like 
those of the higher plants, have two coats, and the embryos are 
dicotyledonous. 

The members of the order, unlike the Conifers, are destitute 
of resinous secretions. 



CHAPTER XII.— THE SPERMATOPHYTA (Continued.) 



THE ANGIOSPERMS, OR ANGIOSPERMS. 

The plants of this class greatly excel the preceding, and in 
fact all others, in the number of their species, and in the variety 
of their habits. There are not less than 125,000 species known. 
They include the great majority of our cultivated plants, most of 
our forest trees, and nearly all our shrubs, herbs, marsh plants 
and flowering aquatics. They are the most highly developed mem- 
bers of the plant kingdom and are best adapted to live as land 
plants. A few among them have acquired parasitic or saprophytic 
habits, and are destitute of chlorophyll, but these are the rare 
exceptions; by far the larger part are chlorophyll-bearing. 

Their tissues are, on the whole, more complex than those of 
Gymnosperms, and their vegetative organs, particularly the leaves, 
are better developed. Their superiority is shown most conspicu- 
ously, however, in the structure of their flowers. In the Gymno- 
sperms, as we have seen, the pollen is brought directly in contact 
with the ovule, but in the Angiosperms the pollen comes in contact 
first with a receptive surface of the carpel known as the Stigma. 
While, therefore, the strobili of the Gymnosperms represent 
flowers in their very simplest form and lack anything resembling 
a calyx or corolla, in Angiosperms, usually, the floral branch, 
including the sporophylls which directly bear the pollen-grains 



CHAPTER XII. — THE ANGIOSPERM^E, OR ANGIOSPERMS. 40!) 

and ovules, and the floral leaves constituting the perianth, exterior 
to them, are much more strongly modified or highly specialized, 
forming a true flower which is more or less conspicuously different 
from the rest of the plant. The perianth is usually differentiated 
into calyx and corolla and serves to protect the sporophylls and 
especially to secure insect pollination. The part of the axis on 
which the floral leaves are borne, is usually very short, and the 
leaves themselves compactly arranged either in whorls or spirals. 
Moreover, the axis nearly ceases its growth after these floral 
leaves are formed, and does not, except in occasional monstrosities, 
produce buds in their axils. The short, often expanded, part of 
the axis, calied the receptacle, that bears the floral leaves, is 
frequently prolonged below T into a stalk or peduncle, which may 
either be naked or bear small modified leaves, the bracteoles. In 
all Gymnosperms, as we have seen, the flowers are either monoe- 
cious or dioecious; but while this is the case also with many Angio- 
sperms, the majority are hermaphrodite, or produce both stamens 
and pistils together in the same flower, the carpellary leaves occu- 
pying the center of the flower, while the stamens are borne imme- 
diately below or exterior to them. But perhaps the most conspicu- 
ous difference between the two Classes, is the fact that, in 
Angiosperms, the ovules are enclosed, while in Gymnosperms they 
are naked or unenclosed. While the pollination in the Gymno- 
sperms is exclusively anemophilous, in the higher Angiosperms it 
is entomophilous. 

Other differences, though less conspicuous and less easily 
detected, but of still greater significance, as showing the relations 
between the tw r o groups, and the connection of both with the 
Pteridophytes, are found in the pollen-grains and embryo-sacs. 

The megasporophylls, here known as carpels, constitute the 
pistil. This organ may consist of one carpel (simple pistil) or of 
a whorl of carpels united together (compound pistil). The ovary, 
the part of the pistil which contains the ovules, and the stigma, 
which receives the pollen, are among the characteristic features 
of the Angiosperms. Within the ovary are borne the megaspor- 
angia, here known as ovules. Each ovule consists of a nucellus 
and two surrounding integuments (already described in Part I). 
The mother-cell of the megaspores is formed within the nucellus 
and, like the microspore mother-cell, undergoes two successive 
divisions, resulting in the formation of four megaspores. Also, at 
one stage of these divisions, a reduction of the chromosomes to the 



410 PART IV. TAXONOMY. 

gametophytic number occurs. One of the megaspores enlarges at the 
expense of the other three, which are used by it as food. The 
adjoining cells of the nucellus are also digested by the growing 
megaspore, whose nucleus divides repeatedly until eight nuclei are 
enclosed within its cell membrane. This constitutes the female 
gametophyte, here known as the embryo- sac. Two so-called polar 
nuclei, one from each end of the embryo-sac, move to the centre of 
the sac and come in contact and may either fuse early or await 
fertilization before fusing. The three nuclei at the micropylar end 
become the egg-cell and the two synergids; the other three nuclei 
comprise the antipodal cells ; now the female gametophyte is ready 
for fertilization. (See Part I, page 107.) 

The microsporophylls, better known as the stamens, consist 
essentially of the microsporangia (pollen-sacs) , of which there are 
usually four in each anther. The microspores (pollen-grains) are 
usually numerous and are formed before the flower opens. As 
in the lower plants, the microspores are formed in special cells, 
known as mother-cells, of which there are many in each pollen-sac. 
While the flower is yet in the early bud stage, the mother-cells are 
formed. Each mother-cell divides twice, forming four pollen- 
grains. This division of the mother-cell nuclei is a reduction divi- 
sion as a result of which the daughter-cells (and therefore the 
pollen-grain nuclei) get only half the number of chromosomes that 
the parent plant (sporophyte) possessed. Before the pollen-grain 
is shed, its nucleus divides, forming two nuclei, known as the 
generative nucleus and the tube nucleus. In this condition the 
pollen reaches the stigma and there resumes its growth or germina- 
tion. 

In the Angiosperms, the germination of the pollen-grain 
(microspore) is simpler than in the Gymnosperms, the prothallial 
cells are absent and the male gametophyte is represented by the 
pollen-tube containing the tube nucleus and generative nucleus, 
the latter dividing to form the two sperms. The pollen-tube (male 
gametophyte) is usually short-lived and exists as a parasite, nour- 
ishes by the stigmatic secretion (see page 106, Part I). 

The female gametophyte, formed in the embryo-sac of Angio- 
sperms, is much more rudimentary than in Gymnosperms, being 
represented only by the egg-cell, two synergids, the three antipodal 
cells and the fusion nucleus. (See Fig. 265, page 107). In fertiliza- 
tion, the stimulus afforded by the union of the second sperm 
nucleus with the fusion nucleus causes a further growth of the 



CHAPTER XIII. — MONOCOTYLEDONES, OR MONOCOTYLEDONS. 411 

prothallus or endosperm, and this with the growing embryo fills 
the sac. Therefore, it is only after fertilization is effected that an 
endosperm is developed in this group of plants. It serves the same 
purpose as the endosperm formed in the embryo-sac of Gymno- 
sperms previous to fertilization, and is called by the same name. 
It is obviously, however, not the same structure but is rather to 
be regarded as a new formation. 

The efforts of botanists to develop a natural classification of 
the Angiosperms have been attended with great difficulties and a 
satisfactory classification is not yet attained. In the attempt to 
follow the lines of evolution the greatest stress has been laid upon 
the structure of the flowers. Those flowers which most closely 
approach the strobili of the Gymnosperms are considered the 
simplest and, therefore, the lowest in evolutionary sequence. 
Flowers without perianths rank below those with perianths. Those 
with the sporophylls arranged spirally are considered simpler than 
those with a cyclic arrangement. Union of petals or carpels repre- 
sents an advance over flowers in which these parts are distinct. 
There is, however, a substantial agreement on the division of the 
Angiosperms into two markedly distinct sub-classes, the Mono- 
cotyledons and the Dicotyledons, in both of which the orders and 
families are arranged in an ascending series. 



CHAPTER XIII.— THE SPERMATOPHYTA. 
THE ANGIOSPERMS (Continued). 



THE MONOCOTYLEDONES, OR MONOCOTYLEDONS. 

Plants of this sub-class seldom show in their stems any distinc- 
tion between wood and bark; they are without medullary rays; 
their fibro-vascular bundles, which are of the closed variety, are 
not arranged radially about a central pith, as are the bundles in 
the stems of Gymnosperms and Dicotyledons, but are irregularly 
imbedded in the fundamental tissue, and there is usually no cam- 
bium zone by which the stems increase in thickness. (See Part II, 
pp. 226.) Only a few tropical species, notably the Palms, become 
trees, the others are mostly herbaceous. 



412 



PART IV. TAXONOMY. 



The primary root, though present in the embryo, in most cases 
soon ceases to grow, and soil solutions are absorbed chiefly by 
adventitious roots, which spring laterally from the stem. More- 
over, these roots possess no cambium zone, have no medullary rays, 
and undergo no important secondary changes as do the roots of 
Dicotyledons, and the central radial bundle commonly has more 
numerous xylem and phloem rays, and the endodermis whic& 
encloses it, is usually composed of thick-walled cells. 




Fig. 612. — Floral diagrams of flowers of Monocotyledons. A, typical flower 
of Monocotyledon; B, diagram of flower of Iris; C, diagram of flower of a Grass. 

The leaves, except those of the Arums, Yams and Smilaxes, 
are seldom reticulate, but are mostly parallel-veined and the 
weaker veins are deeply buried in the mesophyll, and do not stand 
out so prominently on the lower surface as do those of Dicotyle- 
dons ; they are not often opposite or whorled, but usually arranged 
on one of the simpler of the alternate plans, as one-half, one-third 
or one-fourth, though occasionally in a more complex manner; they 
are less commonly provided with stipules than the leaves of Dico- 
tyledons; they are not usually articulated to the stem but are 
commonly sheathing at the base and often with no distinction of 
petiole and blade. Usually they are entire. 

The flowers most commonly have the cycle number of three or 
six and usually consist of five alternating whorls, one of sepals, 
one of petals, two of stamens and one of pistils. See Fig. 612, A. 
In the majority of cases, the perianth whorls, when present, are 
similar in color. 

The seeds, in most cases, possess a copious endosperm, with a 
relatively small embryo, but in some species, as most Orchidacess, 



CHAPTER XIII. — MONOCOTYLEDONES, OR MONOCOTYLEDONS. 413 

no endosperm is formed at all; and in the Alismaceas, Naiadaceai 
and Juncacex, it is formed, but very soon disappears; and in the 
Scitaminales a copious perisperm is developed in its stead. 

But perhaps the most distinctive characteristic of the group 
lies in the structure of the embryo. This is monocotyledonous ; 
that is, instead of an opposite pair of cotyledons, as in many 
Gymnosperms, and nearly all Dicotyledons, only one embryonic 
leaf occurs on the first node; if others are present, they alternate 
with it, and are enfolded by it. As this is the only conspicuous 
one, it is called the cotyledon. The embryo is usually straight and 
cylindrical or obconical, from the thickening of the cotyledon 
toward its upper end, but in a few cases, as in Potamogeton, it is 
elongated and coiled. The axial part (caulicle and radicle) is 
usually very short and nearly enclosed in the relatively large 
cotyledon, but in Sagittaria, Vallisneria, Hydrocharis, and their 
relatives, the axis is more conspicuous than the cotyledon. When 
the seed germinates, in some cases the radicle scarcely grows at 
all, but is almost immediately displaced functionally by adventi- 
tious roots which spring from above it, as in the Grasses; but in 
most cases it grows vigorously for a short time and then stops, 
giving way to adventitious roots. 

The sub-class includes about nine orders, forty families and 
upwards of 24,000 species, and comprises about one-fourth of the 
Angiosperms. 

The first five orders are grouped as the Primitive Monocotyle- 
dons; their flowers are often destitute of perianth (naked) or 
have the floral parts indefinite in number and exhibit spiral rather 
than cyclic arrangements in at least some of their parts. 

Order 1. Pandanales. This order includes three families; the 
Pandanacese, or Screw Pines, the Typhacese, or Cat Tails, and the 
Sparganiaceas, or Bur-reeds. These are the simplest of Monocotyle- 
dons. The perianth is absent; the flowers unisexual and the 
stamens indefinite in number and spirally arranged. The pre- 
dominant family, the Screw Pines, are tropical, the others chiefly 
of temperate regions. 

Order 2. Heliobales. Here are included about one hundred 
species of small herbs mostly growing in water (hydrophytes) or 
in wet places. Among these are the Pondweeds (Potamogeton), 
Water Plantains (Alisma) and Arrowheads (Sagittaria). They 
are chiefly anemophilous or hydrophilous. They present a wide 
range of floral structure, ranking above the Pandanales in that 



414 



PART IV. — TAXONOMY. 



respect. Unlike the following order, they have little or no endo- 
sperm. 

Order 3. Glumales, or Glumiflorae, include two great families, 
the Grasses (Graminese), with nearly 5,000 species, and the Sedges 
(Cyperacese) , with over 2,000. This is among the largest of the 
Angiospermous orders in number of species and no doubt the very 
largest in the number of individuals. The flowers are mostly 
bisexual, destitute of perianth and enclosed by scaly or glumaceous 
bracts. They are mostly arranged in spikes or panicles. The 
fruit of the Grasses is a caryopsis, that of the Sedges, an akene. 




Fig. 613. — Diagram of flower of Butomus, or Flowering-rush, showing a 
doubling in the outer whorl of stamens, and two whorls, instead of one, of pistils. 



The Grasses are the most valuable group of plants from an 
economic standpoint. Fodder for domestic animals and food for 
man are afforded by them. The cereals, including Wheat, Corn, 
Oats, Rice, Rye and Barley, belong here. So also do the Sugar 
Cane and the tropical Bamboo, the latter the only tree in the 
group. The Sedges are distinguished by their solid and mostly 
triangular stems. 

Order 4. Palmales, or Principes, is a well-marked tropical or 
sub-tropical order, including many handsome trees, with upright 
columnar stems crowned by a tuft of frond-like leaves. The family 
Palmaceae,, with about 150 genera and 1,100 species, comprises the 
group, which yields many products of considerable economic 
importance: Dates, Cocoanuts, Sago, Palm Oil, Rattan and Vege- 
table Ivory are among these. In the Palms the perianth is always 
present, the flowers are rather small and occur in simple or 
branched spikes and the inflorescence in its early growth is 
enclosed by a spathe. 



CHAPTER XIII. — MONOCOTYLEDONES, OR MONOCOTYLEDONS. 415 

Order 5. Arales comprise chiefly the family Aracex, with 
about 1,000 species, and the Lemnacese, with only 25. Our Jack-in- 
the-Pulpit or Indian Turnip, the Calla Lily, the Caladiums and 
Anthuriums of our greenhouses and the Sweet Flag (Acorus cala- 
mus) are familiar representatives of the Aroids. The inflorescence 
is usually fleshy, often bearing unisexual flowers, and is character- 
istically surrounded by an enveloping bract or spathe, frequently 
highly colored. In the Lemnacese or Duckweeds is included Wolfna, 
of interest as the smallest of the flowering plants, a tiny green 
grain scarcely larger than a pin head. 

The next two orders are grouped as the Differentiated Mono- 
cotyledons, and in these the individual flower takes precedence 
over the cluster, being larger and more showy than the preceding 
orders. Likewise, the cyclic arrangement of the floral parts now 
predominates and these are usually trimerous and pentacyclic, 
there being commonly three carpels, six stamens (in two whorls) 
and six perianth parts (in two whorls). The showy perianth is 
of service in securing insect pollination. The line of development 
of the group is toward epigyny and zygomorphy. 

Order 6. Farinales, or Bromeliales, includes more than 2,000 
species, over 900 of them comprised in the principal family 
Bromeliacese, largely tropical epiphytes. The Pineapple is a ter- 
restrial member of this family. To the Pontederiaceae belongs the 
common Pickerel Weed of shallow waters ; the Commelinacese yields 
the Spiderwort and the Day Flower. The mealy endosperm which 
characterizes this order is a distinction from the Lilies. 

Order 7. Liliales, including the Lilies and their kin, some 5,000 
species, in nine families, are typical highly developed Monocotyle- 
dons. They are chiefly herbaceous perennials, many of them from 
bulbs. The predominant family is the Liliacese. The Lilies have 
regular flowers with a perianth of six parts and two whorls of 
three stamens each; the three carpels are united; the flowers are 
entomophilous and are often large and showy — some of them 
exceedingly handsome. Lilies, Tulips and Hyacinths belong here, 
as also Onions and Asparagus among our garden vegetables, and 
the medicinal Squill, Aloes, Colchicum and Sarsaparilla. The 
Dragon Tree of the Canary Islands is a liliaceous plant and an 
example of a monocotyledonous stem that increases in diameter 
through the formation of new bundles. The related Amaryllidacese 
yields Amaryllis, Narcissus, Snowdrop, Tuberose and other culti- 
vated flowers, as well as the Agave or Century Plant. The Iridacese 



416 PART IV.— TAXONOMY. 

is the most highly specialized family in the order and yields our 
cultivated Fleur-de-Lis, Crocus and Gladiolus, as well as the 
medicinal Saffron and Orris Root. The Juncacex, including the 
Rushes, grass-like plants growing in water or wet places, are con- 
sidered the lowest of the group. 

The remaining monocotyl orders are classed as the Specialized 
Monocotyledons, by reason of the high degree of specialization 
noticeable in their flowers. The arrangement of the floral parts 
is cyclic and trimerous, but the number of stamens is much reduced 
and the ovary is syncarpous and inferior. The conspicuous peri- 
anth, usually of six parts, is highly irregular, either zygomorphic 
or asymmetrical, and shows distinctive adaptations to insect pol- 
lination. There are two principal orders. 

Order 8. Scitaminales includes the Musacex, Zingiberacex, 
Cannacex and Marantacex. These are chiefly great herbs of 
tropical regions with large clusters of showy flowers. They num- 
ber about 1,200 species. The genus Musa yields the Banana, the 
most popular tropical fruit. The spices, Ginger, Cardamon and 
Turmeric, are products of the Zingiberacex. From the fleshy 
rhizomes of Canna and Maranta species are prepared important 
food starches, known as East Indian and West Indian Arrowroot, 
respectively. The C annas are much grown for ornament. 

Order 9. Orchidales, or Microspermae, includes the family 
Orchidacex, numbering more than 6,000 species and widely known 
for their beautiful and extremely irregular flowers — many of them 
wonderfully adapted for insect pollination. Features of the 
Orchids are: The peculiar lip or labellum, consisting of a large 
petal; the one or two stamens united with the pistil (gyandrous), 
the other stamens being reduced to staminodia or absent entirely; 
the masses of pollen already referred to as pollinia (page 87), 
and the tiny and very numerous seeds. The tropical Orchids are 
the most highly specialized and are mostly epiphytic in habit; 
many of the most prized exotics of our conservatories are among 
them. The Orchids of temperate regions are mostly terrestrial. 
Vanilla "beans," the fruit of a tropical species, is the only economic 
product of importance. Several species of Cypripedium are 
employed in medicine. 



CHAPTER XIV. — THE DICOTYLEDONES, OR DICOTYLEDONS. 417 

CHAPTER XIV.— THE SPERMATOPHYTA. 
THE ANGIOSPERMJE (Continued). 



THE DICOTYLEDONES, OR DICOTYLEDONS. 

The stems of Dicotyledons, like those of Gymnosperms, have the 
collateral vascular bundles arranged radially about a pith, and 
separated from each other by medullary rays, and in nearly all 
cases secondary thickening takes place by means of a cambium 
which lies between the wood and bark, but their tissues are more 
complex, particularly those of the secondary wood, which usually 
consist of wood-cells, wood parenchyma, tracheids and tubes of 
various kinds, and frequently also of some other tissues. The 
branching is always monopodial, and nearly always from axillary 
buds. 

The primary root is often strongly developed, and with its 
branches constitutes the principal root-system of the plant, but 
adventitious roots are also common, and in some instances early 
replace functionally the primary roots, as they do in Monocotyle- 
dons. The roots in most cases undergo important secondary 
changes, increasing in thickness by means of a cambium and devel- 
oping medullary rays resembling those of the stem. The primary 
radial vascular bundle is usually few-rayed, and the walls of the 
endodermal cells which enclose it are seldom thickened. (See Part 
II, page 231.) 

The leaves are remarkable for the variety of their forms and 
modifications; they may be opposite, whorled or alternate, and in 
many cases the phyllotaxy is quite complex; they are frequently 
stipulate, often toothed, incised, or branched into compound forms; 
with very few exceptions, their venation is reticulate, and the 
veins, except in succulent forms, are prominent on the lower 
surface. They are most commonly petiolate, seldom sheathing or 
clasping, and, in most instances, are articulated to the stem. 

The flowers present very great diversity both of form and 
arrangement. In the majority of cases the floral organs consist of 
four alternate whorls, one of sepals, one of petals, one of stamens 
and one of pistils. (See Fig. 614, A). The prevailing cycle num- 
ber is five, but not uncommonly the parts are in fours (see Fig. 
614, C), less frequently they are in twos, threes or sixes. There 



418 



PART IV. — TAXONOMY. 



are, however, numerous deviations from cycle number, due either 
to the suppression of some of the whorls or a part of them, or to 
the multiplication of some of them. The corolla, particularly, is 
liable to be wanting, and the stamens are especially likely to consist 
of multiple whorls. In the Magnoliacese, the Ranuculacese, the 
leafy Calycanthacese and the Nymphseacex, some or all of the floral 
organs may be arranged in spirals rather than whorls. 




Fig. 614. — Floral diagrams of flowers of Dicotyledons. A, diagram of flower 
of Aralia, consisting of four whorls of five alternating parts each ; B, diagram of 
flower of Compositae, calyx wanting (or only represented in the pappus), the 
pistil consisting of two coalesced carpels and five each of the petals and stamens ; 
C, diagram of tetramerous flower of Oleaceae. 



When both whorls of the perianth are present, they are seldom 
alike, but are differentiated into calyx and corolla. Zygomorphic 
and asymmetrical flowers are more common in Dicotyledons than 
in Monocotyledons. 

The embryos of Dicotyledons are relatively large and well 
developed. They may be associated in the seed with a copious 
endosperm, as in the Spurges, Umbelworts and Polygonums, or 
with one which is relatively small in quantity, as in the Mints and 
Milkweeds, or the endosperm may be completely absorbed before 
the seed is ripe, as in the Oaks, Cucumbers, Koses and Cresses. In 
nearly every case it is formed copiously at first, and usually by 
internal cell-formation within the embryo-sac. It is rarely the 
case that the embryo is very rudimentary in the ripe seed, except 
in chlorophylless parasites and saprophytes, such as Monotropa 
and the Orobanchacese, where it often consists of a cluster of only 
a few cells. In the seeds of other species, cotyledons, caulicle, 



CHAPTER XIV. — THE DICOTYLEDONES, OR DICOTYLEDONS. 



419 



radicle and plumule, are usually distinguishable. The plumule, 
though, is sometimes wanting, even in embryos otherwise well 
developed, being represented only by the naked apex of the caulicle 
rising between the bases of the cotyledons, as in the species of 
Cucurbita. The embryos, in nearly all cases, are strictly dicoty- 
ledonous, but, in a few instances, as already explained in Part I, 
they become falsely monocotyledonous or falsely acotyledonous by 
the abortion of one or both of the cotyledons, and it rarely happens, 
on the other hand, that a plant which ordinarily produces a dico- 
tyledonous embryo, develops one with three. This has been known 
to occur in the Oak and Almond. 

In germination, also, the embryo behaves differently from that 
of Monocotyledons, in the relatively strong growth which the 




Fig. 615. — Ricinus communis. A, ripe seed hud open longitudinally; s, testa; 
e, endosperm ; c, cotyledon ; he, hypocotyledonary part of caulicle ; x, strophiole 
or caruncle. B, regminating seed with the cotyledons still buried in the endo- 
sperm, e ; w, primary root ; w', secondary roots. After Sachs. 



primary root or radicle always makes. It pushes out of the seed- 
coats and attains a considerable size, even while the rest of the 
embryo is still contained within the seed. See Fig. 615. The 
cotyledons may either remain enclosed within the seed-coats and 
wither, after the nutriment in them has been exhausted, or they 



420 PART IV. — TAXONOMY. 

may be carried above-ground, performing for a time the functions 
of foliage leaves. * 

The Dicotyledons are chiefly terrestrial mesophytes. To them 
belong all the trees except the Pines and their congeners, and 
nearly all the shrubby plants and a large portion of the herbs 
that constitute the native flora of the northern United States. 
They form by far the largest group of flowering plants, much 
larger, in fact, than all the others combined. About 100,000 species 
are recognized by botanists. They are divided into three principal 
divisions, as follows: 

A. — The Archichlamydese. 
B. — The Polype talse. 
C. — The Sympetalse. 

(A) The Archichlamydeae, or Apetalse, sometimes termed the 
Primitive Dictyledons, have usually small and inconspicuous flow- 
ers, which are mostly destitute of a corolla, and frequently also of 
a calyx. When present these parts are usually rudimentary, 
indefinite in number and spirally arranged. 

Order 1, Verticillales is represented only by the family Casu- 
arinacese, which includes but one genus, Casuarina, and about 20 
species, natives of Australia and southeastern Asia. They are 
trees and shrubs with the aspect of Equisetum. The flowers are 
very simple; the staminate flowers borne in spikes, the pistillate 
in heads. No perianth is present. The ovules contain many 
embryo-sacs instead of one. 

Order 2, Piperales include the Saururacese, Piperacex and 
Chloranthacese. All are destitute of perianth. The Piperacex or 
Pepper Family is much the largest in the order and is noteworthy 
for its aromatic properties. Its members are herbs and shrubs 
with jointed stems, entire leaves, and naked inconspicuous flowers 
in spikes. Pepper, the most largely used of spices, Cubebs and 
Ava Kava, used medicinally, are derived from this family. 

Order 3, Salicales includes the Salicacese or Willow Family. 
The Willows and Poplars, trees and shrubs of temperate and arctic 
regions, with soft white wood and bitter bark, belong here. They 
are dioecious, with both staminate and pistillate flowers in catkins; 
entomophilous ; fruit, a dehiscent many-seeded pod. The barks of 
several species of Willow and Poplar are used medicinally and as 
a source of Salicin, a bitter glucoside. Willow and Poplar woods 
are sources of the medicinal Wood Charcoal. 

Order 4, Myricales, as a group resembles the preceding order, 



CHAPTER XIV. — THE DICOTYLEDONES, OR DICOTYLEDONS. 421 

but the fruit is one-seeded. The Myricacex is the principal family. 
Myrica cerifera yields the Bayberry wax of commerce. Several 
species yield aromatic leaves or astringent barks. 

Order 5, Juglandales is represented by the family Juglandacese, 
a small group of trees and shrubs with odd-pinnate leaves and nut- 
like fruit enclosed in a husk. A number of important food nuts, 
Black Walnut, English Walnut, Butternut, Hickory and Pecan, 
belong here, as well as several valuable woods, including black 
walnut and hickory. 

Order 6, Fagales comprises the families Betulacex and Faga- 
cex, about 700 species in all, and yields many important timber 
trees affording hard woods. These are distinguished from the 
preceding groups by the presence of a" calyx in many of the species. 
In the Fagacese. the pistillate flowers are surrounded by an invo- 
lucre which persists and becomes a "bur" or "cup" in the fruit. 
The volatile oil from Sweet Birch is known in commerce as Oil 
of Wintergreen. Chestnuts and Hazelnuts are important food 
nuts; Beechnuts and Acorns serve as food for animals. Nutgalls 
and Oak Bark, used as astringents and for tanning, Bottle Cork, 
used for stoppers, cork floats, etc., are also products of the Oaks. 

Order 7, Urticales comprises the families Ulmacese, Moracese, 
and Urticacese, distinguished from the preceding six orders by not 
having their flowers in catkins or spikes. The Ulmacese, or Elms, 
are well-known forest trees or shrubs, often cultivated for orna- 
ment. The Moracese, or Mulberries, afford the Fig, Mulberry and 
Bread Fruit, as well as several important fibers, chief among 
which is Hemp. Hops, Lupulin and Indian Hemp are drugs 
derived from the same family. Hempseed yields a bland fixed oil. 
The Urticacese, or Nettles, are chiefly herbs, the common Stinging 
Nettle being one of them. Ramie fiber (Bcehmeria nivea) is an 
important economic product. 

Order 8, Proteales embraces only the family Proteacese, with 
about 1,000 species, natives of the Southern Hemisphere. A few 
are cultivated in our greenhouses for their beautiful flowers. 

Order 9, Santales comprises two families: The Loranthacese, 
or Mistletoes, which are aerial or tree parasites or half -parasites 
in mode of life, and the Santalacese, which are often root-parasites, 
though provided with chlorophyll and therefore at least semi- 
independent. The East Indian Sandalwood (Santalum album) 
yields an odorous volatile oil used in medicine and in perfumery. 

Order 10, Aristolochiales includes the Rafflesias, giant parasites 



422 PART IV. — TAXONOMY. 

already referred to (page 97), and the Aristolochiacex or Birth- 
worts, the latter chiefly herbs or shrubs with erect or twining 
stems. Petals are absent but the gamosepalous calyx is often odd 
in shape and highly colored. Serpentaria and Asarum are official 
drugs derived from this family. Dutchman's Pipe is a rather 
common porch vine. 

Order 11, Polygonales is represented only by the Polygonacese, or 
Buckwheats, comprising about 700 species, including herbs, shrubs 
and trees, mostly native to the temperate regions of the Northern 
Hemisphere. The stipular sheaths and orthotropous seeds are 
distinctive. Buckwheat and Pie Plant among the foods, the 
medicinal Rhubarb and Rumex, and Canaigre, much used in tan- 
ning, are important economic products. 

Order 12, Chenopodiales or Centrospermae includes the families 
Chenopodiacese, Amarantacese, Phytolaccacese, Nyctaginacese, Aizo- 
acese, Portulacacese and Caryophyllacese, which have in common a 
coiled or curved embryo and the fruit not an akene. Over 3,000 
species are embraced in this great order. The Sugar Beet is the 
most important economic plant in the Chenopodiacese, being the 
source of about a half the world's supply of sugar. The tops 
of Spinach, Chard and several other Chenopods are eaten as 
greens. The drug Chenopodium and the oil distilled from it are 
valuable vermifuges. The Amarantacese or Amaranth family 
yields a number of ornamental garden annuals and many weeds of 
cultivated grounds. The Nyctaginacese or Four-0 'Clock Family 
yields several garden plants, among them the Bougainvillea and 
Four-0 'Clock. The Phytolaccacese is represented in medicine by 
the Poke, the root of which is employed. Aizoacese includes the 
Ice Plant (Mesembryanthemum crystallinum) , which has leaves 
covered with hairs bearing a viscid liquid and giving the plant a 
characteristic frosty appearance. The Portulacacese yields a num- 
ber of mucilaginous plants, several of them being used as pot- 
herbs. The Caryophyllacese, a large and widely distributed family, 
furnishes several of our cultivated flowers, Dianthus, Gypsophila, 
Lychnis and Saponaria. 

(B) The Polypetalae, or Dialypetalae, sometimes termed the 
Differentiated Dicotyledons, have better developed individual flow- 
ers, usually in four whorls, with the calyx green in color, and 
distinguished thereby from the corolla. The petals are usually five 
in number and distinct. Entomophily is the prevalent form of 
pollination. 



CHAPTER XIV. — THE DICOTYLEDONES, OR DICOTYLEDONS. 423 

Order 13, Ranales is characterized by having, usually, separate 
petals, sepals, stamens and carpels, the two latter often more 
numerous than the petals. About 3,000 species are included in the 
f ollowing nine families : Nymphacese, or Water Lily family, aquatic 
plants, among them the Lotus and White Pond Lily, as well as the 
Amazonian Victoria regia. Renunculaceae, or Buttercup Family, 
which includes several important drugs, notably Hydrastis and 
Aconite. The Columbine, Larkspur, Anemone, Clematis and Peony 
are familiar ornamental plants belonging to this family. Berberi- 
dacese, or Barberry Family yields the Podophyllum or May Apple, 
of which the resin from the underground parts is a valuable 
cathartic, also the ornamental Barberries (Berberis), whose root- 
bark contains the bitter yellow alkaloid Berberine. Menisperma- 
cese, or Moonseed Family furnishes Calumba, much used as a bitter 
tonic, also the poisonous Fish Berries (Anamirta Cocculus). 
Magnoliacex, or Magnolia Family includes the Magnolias and other 
trees and shrubs with handsome flowers. Calycanthacex supplies 
a number of ornamental shrubs. Anonacex, mostly tropical, 
yields several edible fruits, including the Northern Pap aw (Asi- 
mina). Myristicacese, a small tropical family, furnishes the valu- 
able spices, Nutmeg and Mace, the latter being the aril and the 
former the kernel from the same fruit. Monimiacex, a tropical 
and subtropical family of trees and shrubs, supplies the medicinal 
Boldo leaves. Lauracese, or Laurel Family is rich in useful plants. 
Among its products are Camphor, Cinnamon and Sassafras. The 
Sweet Bay and the Avocado also belong here. 

Order 14, Papaverales, or Ehceadales, comprise more than 2,000 
species, mostly herbs, which are distinguished from the preceding 
order chiefly by their united carpels, forming a compound ovary. 
Papaveracex affords Opium, noted for its sedative and narcotic 
properties, also Sanguinaria and Celandine, which are medicinal, 
as well as several varieties of Poppy cultivated for ornament. 
Fumariacess gives several well-known garden plants, including the 
Bleeding Heart (Dicentra) . Cruciferx, named from its four 
petals, which form a cross, yields both black and white Mustard, 
Cabbage, Turnip, Rutabaga, Radish and other useful products. 
This family numbers 1,600 species and is characterized by its four 
petals, six stamens (four long and two short), its pod-like fruit 
(Silique or Silicle), the peculiarly curved embryo and the acrid, 
watery juice. Capparidacese, closely related to Cruciferae, fur- 
nishes the cultivated Caper (Capparis) and several garden plants. 



424 ' PART IV. — TAXONOMY. 

Resedacese, or Mignonette Family and Moringacese, or Moringa 
Family are small groups yielding little of importance. 

Order 15, Sarraceniales includes a small group of perennial 
herbs growing in bogs and insectivorous in habit. Among the 
families are Sarraceniacess, the American Pitcher Plants, Nepen- 
thacese, or East Indian Pitcher Plants, and Droseracese, or Sundews. 
Several species are employed in medicine, otherwise they are of 
little economic importance. (See Figs. 131, 133 and 134, page 53.) 

Order 16, Rosales comprises a very large and varied order of 
about 10,000 species, yielding many important economic products. 
Crassulacex or Orpine Family is composed chiefly of succulent 
plants whose water-storing facilities fit them for dry climates. 
Saxifragacese yields the Currants and Gooseberries, as well as the 
Philadelphus, Hydrangea and other ornamental shrubs and herbs. 
Pittosporacese comprises a group of Australian plants; several 
species, chiefly evergreen shrubs, are in cultivation. Hamamelida- 
cese furnish our Witch Hazel and Sweet Gum tree (Liquidambar) ; 
Styrax, a medicinal balsam, is obtained from an Asiatic species of 
Liquidambar. Platanacex includes the Plane Tree (Platanus) 
and the Button-Ball {C ephalanthus) . 

Rosacea* is a large family of 1,500 species. Many of the flowers 
resemble those of the Ranunculaceze, but are perigynous, the sepals 
united or confluent with the cup of the receptacle upon which the 
petals and stamens are borne. The family is usually divided into 
several sub-families based on the nature of the fruits; one having 
follicles; another pomes; a third, achenes or separate drupelets, 
and a fourth, drupes. To the Rosacese belong many cultivated 
fruits, the Apple, Pear, Quince, Cherry, Plum, Peach, Raspberry, 
Blackberry and Strawberry. Also many ornamental plants, Roses, 
Hawthorne and Spiraeas, and a considerable number of medicinal 
plants, Wild Cherry, Soapbark, Bitter Almond and others. Legn- 
minosx, one of the largest families in the plant kingdom, comprises 
about 7,000 species and is widely distributed, though more abun- 
dant in the tropics. It is usually divided into three sub-families: 
Mimosas, with regular flowers; C&salpinse, with irregular but not 
papilionaceous flowers, and Papilionacese, with papilionaceous 
flowers (see Fig. 181, page 79). The common character is the 
leguminous fruit (see Fig. 226, page 89). The leaves of many 
of the Leguminosse are motile (see page 287), and the pollination 
often quite intricate. The roots often bear tubercles con- 
taining nitrogen-fixing bacteria (Fig. 497). Peas and Beans 



CHAPTER XIV. — THE DICOTYLEDONES, OR DICOTYLEDONS. 425 

among food plants; Clovers and Alfalfa among forage plants; 
Logwood and Red Saunders among dyestuffs; Acacia and Traga- 
canth among the gums; Kino and Catechu among astringent 
medicines, Balsams of Peru and Tolu, Licorice, Copaiba and other 
drugs, including the very poisonous Calabar Bean (Phystostigma) , 
are a few of the immense number of economic products of this 
family. 

Order 17, Geraniales is another large and varied order including 
some 8,000 species. It is distinguished from the preceding order 
by its compound pistils and usually separate sepals. The families 
embraced in it are: Geraniacese or Geranium Family, to which the 
Wild Geranium and the house Geranium (Pelargonium) belong; 
Oxalidaceae or Oxalis Family; Tropaeolacese or Nasturtium Family; 
Linacese, which yields Flax, with its valuable fiber and seed-oil; 
Erythroxylacese, from which the Coca leaf and its habit-forming 
alkaloid, Cocaine, are obtained; Zygophyllacese, represented in 
medicine by Lignum Vitse and its resin, Guaiac; Rutaceas, yielding 
the important Citrus fruits, Oranges, Lemons, Limes and Grape 
Fruit, as well as the medicinal Buchu, Pilocarpus and Prickly Ash; 
Simarubacese, from which the bitter Quassia wood is obtained; 
Burseracese, which supplies the fragrant gum-resins Myrrh, Oliba- 
num and Frankincense; Meliacese, furnishing Mahogany and West 
Indian Cedar as well as the Pride of India and other ornamental 
southern trees; Polygalacese, affording the medicinal Senega, and 
Euphorbiacess or Spurge Family, in which the apparently single 
blossoms are really clusters of reduced flowers, often monoecious 
or dioecious, and surrounded by highly colored bracts which sim- 
ulate petals (e. g., Poinsettia). The Spurges comprise about 4,000 
species and among their valuable products are India Rubber, 
Cassava, Castor Oil, Croton Oil and many useful and ornamental 
plants. 

Order 18, Sapindales embraces about 2,500 species, mostly trees 
and shrubs belonging to the following families : Buxacese, to which 
the ornamental Box belongs; Empetracete, or Crowberry Family; 
Coriariacese, which yields the poisonous Myrtle-leaved Sumach of 
Southeastern Europe; Limnanthacese ; Anacardiacese, to which 
belongs the Pistachio-nut, the Cashew-nut, the Mango, the orna- 
mental Pepper Tree and Sumach, and the Poison Ivy; Aquifoliaceze, 
from which comes the Holly used in Christmas decoration; Celas- 
tracese or Staff Tree Family, including several ornamental shrubs 
with showy arillate seeds; Staphyleacese or Bladdernut Family; 



426 PART IV. — TAXONOMY. 

Aceracese, including the Maples; Hippocastanacem, including the 
Horse-chestnuts; Sapindacess, yielding the Soapberry and the 
medicinal Guarana, and Bahaminacese, represented by the familiar 
Touch-me-not and Balsam. 

Order 19, Rhamnales includes about 1,000 species, mostly 
shrubs, small trees or vines. Its families are: Rhamnacex, includ- 
ing the cathartic Cascara and Frangula barks, as well as the 
Buckthorns, and Vitacex, to which the Grape, the Virginia Creeper 
and the Boston Ivy belong. 

Order 20, Malvales comprises about 2,100 species of herbs, 
shrubs and trees, including: the tropical family Elseocarpacese; 
Tiliacese, represented by the Linden or Basswood trees; Malvacese, 
yielding the invaluable Cotton with its seed-hairs and bland oil; 
Bombacess, to which belongs the Baobab and the Silk-Cotton trees; 
and Sterculiaceze, furnishing Chocolate and Cacao Butter as well 
as the caffeine-containing Cola. 

Order 21, Parietales, comprising about 3,000 species, is related 
to the Rosales, from which it differs chiefly in having parietal pla- 
centas (Fig. 232, page 91). Many of the species are tropical 
or subtropical. Among the families of this order are Theacese, 
or Tea Family; Guttiferse, from which the medicinal Gamboge is 
obtained; Hypericaeese, represented by St. John's wort and St. 
Peter's wort; Tamaricacese, including the cultivated Tamarisk; 
Cistacese, or Rock Rose Family; Bixacese, which furnishes the 
Annatto of commerce; Violacese, including the Violets and Pansies; 
Passifloraceze or Passion-flower Family; Caricacese, which yields 
the tropical Pawpaw containing a pepsin-like ferment in its juice, 
and Begoniacese, represented by the Begonias, which are among 
our highly prized ornamental plants. 

Order 22, Opuntiales, represented by a single family Cacta- 
cese, including about 1,200 species, nearly all being American. They 
are fleshy plants with large and showy flowers. Their character- 
istic spines are modified leaves. The Night Blooming Cereus is 
grown in greenhouses for its beautiful flowers ; its succulent stems 
are used in medicine. Mescale buttons (Anhalonium) are used as 
narcotics and intoxicants by certain Indian tribes. The fruits of 
the Indian Fig are edible. Many species, owing to their water- 
storing ability, are adapted to desert conditions. 

Order 23, Myrtales includes 7,500 species, chiefly tropical. 
Among the families represented are: Thymeleacese, yielding the 
medicinal Mezereum; Elasagyiacese, furnishing several cultivated 



CHAPTER XIV. — THE DICOTYLEDONES, OR DICOTYLEDONS. 427 

ornamental shrubs, among them the Shepherdia; Lythracess, repre- 
sented by several garden plants, including the Crape Myrtle, and 
also yielding Henna, used as a red dye for the hair; Punicacese, 
from which the Pomegranate is obtained; Lecythidacex, yielding 
the Brazil-nut and other oily edible seeds; Rhizophoracess or Man- 
grove Family, remarkable for the serial roots borne by its mem- 
bers; Combretacese, which yields several useful hard woods; 
Myrtacese, a large tropical family rich in aromatic volatile oils, 
such as Oil of Cajuput and Oil of Bay, and the source of the 
well-known spices Cloves and Allspice. The Australian genus 
Eucalyptus yields a variety of volatile oils, as well as astringent 
extracts and valuable hard-woods. Among the Eucalypts are the 
tallest trees known. The Guava and Rose Apples, prized in the 
tropics, are myrtaceous fruits; Melastomacese, another large trop- 
ical family, yields little of economic value, though several species 
are cultivated for the beauty of their flowers; Onagracese includes 
the Evening Primrose (Oenothera), Fuchsia and Willow Herb; 
Hydrocaryacese or Water Chestnut Family, and Haloragidaceas, 
a group of aquatic or terrestrial herbs, including Myriophyllum, 
conclude the order. 

Order 24, Umbellales, or Umbelliflorae, numbers about 2,000 
species, comprised in three families. Small, epigynous flowers are 
common to the order. Araliacese yields the Ginseng, so highly 
prized in Chinese medicine, the English Ivy (Hedera) , cultivated 
for ornament, the Spikenard, and some other medicinal or orna- 
mental Aralias. Umbelliferge, named from the prevalent flower 
cluster (see Fig. 154, page 64) , is a family of about 1,500 species, 
distinguished by well-marked characters; the epigynous flower 
with five petals and five stamens attached to a fleshy epigynous 
disk. (See Fig. 174, page 76) ; and the peculiar double fruit 
(cremocarp) (see Fig. 286, page 117). There are many useful 
products of this family. Among the spices are Anise, Caraway, 
Coriander, Fennel and Dill; among the vegetables, Carrot, Celery 
and Parsnip; among the drugs, Asafcetida, Ammoniac, Galbanum, 
Lovage and Sanicle. A few, such as Poison Hemlock (Conium) , 
Fool's Parsley (JEthusa) and Water Hemlock (Cicuta) are seda- 
tive poisons. Cornacex is distinguished from the preceding family 
by not having the flowers in umbels; many species have the flowers 
in heads surrounded by a large, petaloid involucre. Several species 
of Coimus (Dogwood) are grown as ornamental shrubs. 

(C) The Sympetalae or Gamopetalae, is named from the most 



428 PART IV. — TAXONOMY. 

prominent character, the union of the petals; this coherence may, 
however, be slight, or even lacking in some families. The group 
is also known as the Metachlamydese or as the Specialized Dicotyle- 
dons. The flowers are mostly epigynous or perigynous, with the 
corolla and stamens attached to the tube of the calyx. They are 
commonly entomophilous and showy. In the Isocarpic subdivision, 
the carpels of the compound ovary equal in number the petals and 
sepals and are half as numerous as the stamens, there being 
usually five carpels, ten stamens, five petals and five sepals. In 
the Anisocarpic subdivision there are usually two carpels, five 
sepals, five petals and five stamens. 

Order 25, Ericales includes about 1,800 species, mostly shrubs, 
many evergreen, and characterized by the stamens being mostly 
free from the corolla or attached only to its base. Six families are 
usually distinguished. Clethraceae has a superior, three-celled 
ovary and a corolla of five separate petals. The plants are mostly 
tall shrubs or small trees with deciduous leaves. A few species 
are grown for ornament. Pyrolacex is distinguished from the 
preceding family by the usually four- to five-celled ovary and 
evergreen foliage. Several species of Chimaphila and Pyrola are 
used in medicine. Monotropacex is of interest by reason of the 
saprophytic habit of its members, of which the Indian Pipe (Mono- 
tropa uniflora) is representative. Ericaceae, or Heath Family is 
much the largest in the order, comprising about 1,400 species, 
mostly shrubs, many with evergreen leaves and all (except Ledum) 
with gamopetalous corollas. The stamens are often appendaged 
and dehisce by terminal pores (see Fig. 207, page 84). Arctosta- 
phylos Uva-Ursi and related species are used medicinally; Cran- 
berries, Blueberries and Huckleberries are valuable fruits; Rhodo- 
dendrons are cultivated for their beautiful flowers; Gaultheria 
procumbens is the source of Oil of Wintergreen, used as a flavor 
and in medicine; several species of Kalmia contain poisonous prin- 
ciples, Trailing Arbutus (Epigea) is a favorite spring flower. 
The Heathers (Calluna) and Heaths (Erica) are well-known 
European genera. The Epacridacex are shrubs or small trees 
native to Australia and New Zealand. Diapensiaceas is a small 
family of low shrubs, among them the Pyxie or flowering Moss 
(Pyxidanthera) . 

Order 26, Primulales comprises about 1,100 species, many trop- 
ical, our species being herbs, with regular, perfect flowers, the 
stamens borne on the corolla and as many as its lobes and opposite 



CHAPTER XIV. — THE DICOTYLEDONES, OR DICOTYLEDONS. 429 

them. There are three families. Myrsinaceas is a tropical family 
yielding little of importance. Primulacese includes the true Prim- 
roses, Cyclamen, 'and several other ornamental plants. Of Plumba- 
ginacex, a few genera are represented by garden flowers, such as 
Armeria and Statice. 

Order 27, Ebenales, about 1,000 species of trees and shrubs, 
chiefly tropical, includes: Sapotacex, from which Gutta Percha 
and Chicle Gum are obtained; Ebenacea?, yielding the valuable 
Ebony wood, and the cultivated Japanese Persimmon, as well as 
the native Persimmon; Styraceae, from which is obtained a balsamic 
resin known as Benzoin, official in our pharmacopeia, and Symplo- 
cacese, an East Indian family represented in North America by 
only one species and yielding little of economic value. 

Order 28, Gentianales, or Contortae, a large group of about 
4,400 species, having usually two distinct ovaries or a compound 
ovary with two cavities ; the stamens mostly attached to the corolla 
tube. There are five families: Oleacese, trees or shrubs, includes 
the Olive, cultivated from the earliest times for its fruit and its 
oil; the Manna Ash, the saccharine exudation of which is employed 
in medicine, and several cultivated ornamental shrubs, among them 
Lilac, Privet, White Jasmine, Forsythia and Chionanthus.. Logania- 
cese, chiefly tropical, yields several valuable medicines, among 
them Nux Vomica and Ignatia seeds, both of which contain the 
very poisonous alkaloid Strychnine; here also belongs Spigelia, 
employed as a vermifuge, and Gelsemium or Yellow Jasmine, a 
poisonous drug used as a nervine. Gentianaceae, mostly herbs 
with bitter juice, the ovary one-celled, and the leaves exstipulate, 
yields the official Gentian, a bitter tonic drug; also Menyanthes, 
Chirata, Sabbatia and Frasera, used similarly, and our native 
Gentians, among the most handsome of our wild flowers; Apocyna- 
ceae, with a milky juice, sagittate anthers, usually two separate 
ovaries but with the stigmas and styles united are chiefly trop- 
ical; several species yield Rubber, and quite a few are poisonous; 
the medicinal Strophanthus, a powerful heart tonic, employed by 
the African natives as an arrow poison belongs here, also the 
rhizomes of several species of Apocynum, used medicinally, like- 
wise the bark of the South American tree Aspidosperma Quebracho- 
bianco. Asclepiadacese, also with a milky juice, are distinguished 
from the preceding by their distinct styles, monadelphous stamens, 
and pollinia (see Fig. 221, page 87). Here belong our common 



430 PART IV. — TAXONOMY. 

Milkweeds, Pleurisy Boot (Asclepias tuberosa) and the South 
American Condurango Bark, used medicinally. 

Order 29, Polemoniales, or Tubiflorse, a very large group com- 
prises about 13,500 species of herbs, shrubs and trees, having a 
compound ovary, flowers regular or irregular, stamens mostly 
adnate to the middle of the corolla tube or beyond. There are 
eighteen families. Convolvulacex yields the powerfully purgative 
Jalap and Scammony roots, the edible Sweet Potato, the orna- 
mental Moonflower, Morning Glory and Cypress Vine and the 
parasitic Dodders (Cascuta) and Bindweeds which do much dam- 
age to some crops. Polemoniacese is represented among garden 
plants by the Phloxes, Cobsea, and Polemonium. Hydrophyllacese 
affords us Yerba Santa, used in medicine, and several ornamental 
plants. Boraginacex yields many plants which were formerly used 
in medicine but now have been dropped from use as being of little 
value. Alkanet root, used as a dye ; Heliotrope and Forget-me-not, 
familiar garden plants, belong here. The Verbenacese includes 
the Vervain (Verbena hastata) and others used in medicine, 
though now considered of little value; also several ornamental 
herbs or shrubs, Lantana, Lippia and Verbena. Labiatse, compris- 
ing herbs or shrubs with square stems, mostly bilabiate corollas, 
four (didynamous) or only two stamens, and a superior ovary of 
two carpels, deeply four-celled, are noted for their aromatic volatile 
oils. Owing to these essential oils and to bitter principles, many 
are employed in medicine, among them Peppermint, Spearmint, 
Scutellaria, Thyme, Rosemary, Lavender and Catnip. Thymol, 
prepared from Oil of Thyme, is a valuable antiseptic and parasiti- 
cide. Menthol, from Oil of Peppermint, is a useful anodyne. Sage, 
Marjoram and Savory are used for culinary purposes. Many 
species are cultivated for ornament or for their odor and flavor or 
for medicinal use. Nolanacese is a small South American family. 
Solanacea? is important as the source of the Potato, Tomato, Egg 
Plant, Cayenne Pepper and Tobacco. It also yields the poisonous 
drugs Belladonna, Hyoscyamus and Scopola, which contain mydri- 
atic alkaloids and are powerfully sedative. A number of trouble- 
some weeds, Black Nightshade, Jimson Weed and Horse Nettle, 
belong here. About thirty genera are cultivated either for food, 
medicine or ornament. Scrophulariacese affords many plants of 
medicinal value; Digitalis, a powerful and poisonous heart tonic, 
and Leptandra, a cathartic drug, are among them. Many species 
are cultivated for their showy flowers, notably Snap-dragon, Cal- 



CHAPTER XIV. — THE DICOTYLEDONES, OR DICOTYLEDONS. 431 

ceolaria, Chelone, Foxglove, Linaria, Mimulus and Veronica. 
Bignoniaceaz, mostly tropical woody climbers, are of small eco- 
nomic value; our Catalpa trees and Trumpet Flower belong here. 
Pedaliacese, is a small family of herbs, natives of Africa, southern 
Asia and Australia; the foliage bears mucilage-secreting glands. 
Oil of Sesame, from the seed of Sesamum indicum, is a fatty oil of 
considerable importance. Martyniacese. is a small family, native to 
tropical and subtropical America and of little or no economic 
importance. Gesneriacese, though widely distributed, yields little 
of value except a few ornamental plants. Lentibuliariacex includes 
the Butterwort (Pinguicula) and Bladderwort (Utricularia) and 
other insectivorous plants, mostly aquatic. Globulariacese is a 
small family native to the Mediterranean region. Acanthaceae, 
comprising about 1,500 species, yields little of interest excepting a 
few ornamental herbs and shrubs. Myoporacex is a small family 
of tropical or subtropical shrubs or trees and of little economic 
interest. Phrymaceze comprises a single genus and but one species, 
an ornamental plant. 

Order 30, Plantaginales includes only the Plantain Family 
(Plantaginacese) , a small but widely distributed group of about 
200 species. A few were formerly used in medicine but have been 
discarded as of little value. The common Plantain (Plantago) is 
a weed in lawns and dooryards. 

Order 31, Rubiales comprises about 5,300 species, mostly trop- 
ical and of considerable economic importance. By far the largest 
family is Rubiacese, with 4,500 species. They include herbs, shrubs 
and trees with epigynous flowers and with stamens and lobes of 
the calyx and of the corolla, usually four to five. Among its 
valuable products are Coffee, Cinchona bark and Quinine, Ipecac 
and Gambir. The family is mostly tropical, but many species are 
cultivated in greenhouses, one of them being the Gardenia. Among 
the native species are Buttonbush (Cephalanthus) , Cleavers 
(Galium), Bluets (Houstonia) and Mitchella (see Fig. 255, page 
101). Caprifoliacese includes the Honeysuckles, Elders and Vibur- 
nums, also the Snowberry (Symphoricarpos) , Twin Flower (Lin- 
nea) and Horse Gentian (Triosteum). Several are used medi- 
cinally but are not powerful drugs. Valerianacex gives us the 
antispasmodic drug, Valerian, noted for its peculiar odor. Dip- 
saceae yields the Fuller's Teasel (Dipsacus ferox), the spiny, 
hooked bracts of which are used in "fulling" cloth. 

Order 32, Campanulales include an immense assemblage of over 



432 PART IV. — TAXONOMY. 

13,000 species, highly specialized as regards the consolidation of 
the parts of the flower. With a few exceptions, the anthers are 
united (see Fig. 201, page 83). The Cucurbitacese. are monoecious 
or dioecious and the flowers are not in heads. These are herbs, or 
rarely shrubs, tendril-bearing and climbing and with characteristic 
melon fruits. Here belong the Pumpkin, Squash, Watermelon, 
Muskmelon and Cucumber, also the Luffa or Vegetable Sponge, the 
Gourd or Calabash, and a number of powerful cathartic drugs, 
some of them poisonous. Among these are Colocynth, Bryony and 
Elaterium. The Campanulacese numbers about 1,500 species, with 
gamopetalous and epigynous flowers, many ovules and often united 
stamens. Lobelia inflata is an official drug and is acrid and some- 
what poisonous. The Blue Lobelia, the Cardinal Flower, the Bal- 
loon Flower (Platycodon) and the Bluebell (Campanula) are 
among the ornamental plants of this family. The Composite is 
much the largest family, including between 10,000 and 12,000 
species, characterized by having their flowers in involucrate heads 
(see Fig. 150, page 63). The corolla is commonly tubular or ligu- 
late and the five stamens are attached to it and usually have their 
anthers united in a ring around the style. The calyx is often 
reduced to a tuft of hair termed a pappus. They are mostly herbs, 
with a few shrubs. While many of the Composite have been 
employed medicinally, yet the number of valuable drugs is not 
large. Included in the official list are Dandelion Root (Taraxa- 
cum), Lactucarium (from Lactuca virosa), Grindelia, Eupatorium, 
Pyrethrum, Santonin (from Artemisia pauciflora) , Arnica, Lappa, 
Calendula, Matricaria, Absinthium, Inula, Echinacea and Farfara. 
Insect powder is the powdered flower heads of two species of 
Chrysanthemum. Rather few are used for food,; Lettuce, Oyster 
Plant, Chicory, Globe Artichoke and Jerusalem Artichoke are the 
most important. A large number are cultivated for the beauty of 
their flowers; Asters, Chrysanthemums, Daisies, Dahlias, Mari- 
gold, Cinerarias, Sunflowers, Goldenrods and Zinnias among them. 
Many are obnoxious weeds; the Thistles, Cockle Burs and Bur- 
docks are the most common. 



CHAPTER XV.— EVOLUTION. 



DARWINISM. — VARIATIONS. — MUTATIONS. 

In discussing the classification of plants, in the foregoing 
chapters, it was assumed that relatively simple groups of plants 



CHAPTER XV.— EVOLUTION. 133 

preceded those of more complex structure. This view accords with 
the results of the study of fossil plants as well as living forms. 
It is not controverted by the fact that some simple forms of plants 
now existing, have developed from more highly organized ances- 
tors. These changes in living organisms, whether progressive, as 
in passing from the simpler to the more complex, or regressive, 
when this order is reversed, constitute what is termed Evolution. 

Evolution is, then, a gradual but constant change, in operation 
since the very beginning of things and still going on. Not only are 
living organisms, plants and animals, undergoing these changes; 
they occur as well with inorganic things. Seacoasts are washed 
away or are added to; mountains are worn down; certain areas of 
the earth's surface have been elevated and other areas lowered; 
regions that had in early ages a tropical climate are now temper- 
ate or, perhaps, arctic. Even the elements themselves have not 
escaped, for modern researches indicate that radio-activity com- 
prises, essentially, changes in the chemical elements, hitherto 
deemed unchangeable. These changes in the non-living material 
of the earth, have affected fundamentally the development of 
plants and animals, so that inorganic evolution and organic evolu- 
tion have, in a measure, gone on together. In living organisms, 
such as plants, these changes fall into two classes: those which 
occur during the course of life of the individual plant, from the 
spore to the fully developed structure, known as ontogenetic, and 
those which accompany the development of a group of related 
plants, phylogenetic changes. Ontogeny, then, considers the life 
history of the individual ; phylogeny traces the ancestral history of 
the race. There is a remarkable parallel between ontogenetic and 
phylogenetic changes and it is a well-supported scientific fact that 
"ontogeny epitomizes phylogeny" and the life history of the indi- 
vidual gives a clue to the development of the race. But while 
evolution is now accepted universally as a fact, the method by 
which evolution is effected is still undetermined. 

The French naturalist, Lamarck, having made certain observa- 
tions, such as that the muscles and some of the organs of man and 
of animals are enlarged and strengthened by use and that through 
lack of exercise they lessen or even become lost, undertook to 
explain the manner by which evolution takes place by assuming: 
that plants and animals have been exposed to a constantly chang- 
ing environment; that they have undergone changes in structure 
to fit them for their altered environment; and that these changes 



434 PART IV. — TAXONOMY. 

induced by environment have become hereditary and are intensified 
in passing from generation to generation. However, the evidence 
accumulated since Lamarck's time shows that the changes in ani- 
mals and man, resulting from use or disuse of organs, are not 
inherited, much less are they added to in passing from parent to 
offspring. In plants, also, it seems now quite certain that most 
modifications that result directly from environment, are not 
inheritable. 

Darwinism. Darwin's studies, extending over a period of more 
than twenty years and culminating in the publication of his great 
book, the Origin of Species, presented a most convincing argument 
for evolution and profoundly influenced scientific thought. His 
fundamental propositions are that evolution is the method of 
creation, and the method of evolution is based on "natural selec- 
tion." 

His theory of natural selection might well be termed the essence 
of Darwinism. It is based upon several fundamental facts: First, 
that parental characters tend to reappear in succeeding genera- 
tions. The resemblance of children to their parents or grand- 
parents in features or temperament is a familiar observation; 
evidently there is an inheritance of physical or of mental charac- 
ters, one or both. Second, that this inheritance is never complete. 
Always there is some variation. The child resembles but is never 
the replica of the parent; there may be a resemblance to one 
ancestor in the color of the eyes and to another in the shape of 
the face. Among plants, there may be variations in height, in 
•the number of flowers borne by the plant, in the colors of the petals 
or in the shape of the leaves. Now it may happen that some of 
these variations are such that they better fit the plant to the 
conditions of its environment and hence are of direct advantage 
to it. Other variations, on the contrary, may be detrimental. 
Those individuals that develop favorable variations have an advan- 
tage in maintaining themselves and in propagating their kind. 
Through successive generations, the advantageous inheritance is 
intensified and may finally become a character of a new species. 
Darwin's observations and experiments convinced him that through 
continuous selection of variants it is possible to secure plants 
having certain desired characters. In this he was following along 
lines of plant and animal breeding under domestication. As com- 
pared with such artificial selection, Darwin argued that natural 
causes, notably severe competition between individuals of the same 



CHAPTER XV. — DARWINISM. 435 

species, as well as between different species occupying the same 
habitats, would give similar results, these he termed natural 
selection. 

The Struggle for Existence, Darwin used this term, to include 
not only the existence of the individual as such but also success in 
perpetuating its kind. "Two canine animals in time of dearth may 
be truly said to struggle with each other which shall get food and 
live. But a plant on the edge of a desert is said to struggle for 
life against the drought, though more properly it should be said 
to be dependent on moisture. A plant which annually produces 
a thousand seeds, of which only one on an average comes to 
maturity, may be truly said to struggle with other plants of the 
same and other kinds which already clothe the ground." Darwin 
showed that "every being, which during its natural lifetime pro- 
duces several eggs or seeds, must suffer destruction during some 
period of its life or during some season or occasional year; other- 
wise, on the principle of geometrical increase, its numbers would 
quickly become so inordinately great that no country could support 
the product." Some of our weeds produce annually as many as 
25,000 seeds from a single plant. If all of these seeds grew into 
plants and the same with succeeding generations, their progeny 
would in a few years be sufficient to cover the inhabitable portion 
of the earth. Yet, while certain plants may increase very rapidly 
for a time, in the end their spread is checked and from that time 
their numbers remain stationary or decrease. Darwin cites the 
results of observations on a piece of ground six square feet in area, 
dug and cleared, and where, out of 357 seedlings of native weeds 
as they came up, 295 were destroyed by slugs and insects, and in a 
little plot of mown turf, 12 square feet in area, nine out of twenty 
species were killed by the other species being allowed to grow up 
freely. 

Survival of the Fittest. In the severe competition between all 
living organisms and especially between those of the same kind 
and habit, the advantage lies ultimately with those whose varia- 
tions happen to be such as to better fit them for this struggle. 
Since many more individuals are born than can possibly survive, 
those having any advantage, however slight, over the others, have 
the best chance to live and to reproduce their kind. A plant whose 
variation takes the form of increased height will grow out from 
the shade of its neighbors and receive more light. Also it will 
develop a correspondingly more extensive root system and secure 



486 , PART IV. — TAXONOMY. 

more water from the soil. So it is, likewise, with plants develop- 
ing a greater thickness of epidermis, as a defense against too great 
transpiration, or an unusually heavy growth of hairs, or any of 
the multitude of floral devices which favor cross-fertilization and 
hence the production of a more vigorous offspring. The perpetua- 
tion and increase of such advantageous variations is comprised in 
what Darwin called Natural Selection, but which Herbert Spencer 
forcefully termed "the survival of the fittest." It might more 
accurately be described as the elimination of the unfit, for it is this 
process of elimination that leaves room and food supplies for the 
best-adapted individuals to live and propagate and eventually 
results in the development of new species. 

Objections and Difficulties. The publication of the "Origin of 
Species" brought upon its author the severe criticism of many 
theologians who thought that the foundations of religion were 
endangered. But Darwin disclaimed the intention of shocking the 
religious feelings of anyone. He called attention to the fact that 
the discovery of the law of the attraction of gravity had been 
similarly attacked by Leibnitz as "subversive of natural, and infer- 
entially of revealed religion." He states, "A celebrated author 
and divine has written to me that he has gradually learned to see 
that it is just as noble a conception of the Deity to believe that 
He created a few original forms capable of self -development into 
other and needful forms, as to believe that He required a fresh 
act of creation to supply the voids caused by the action of His 
laws." Other objections and difficulties have been raised by scien- 
tists and some of these have not yet been satisfactorily answered. 
Among them are the absence of transitional forms or "connecting 
links" between related species; the inheritance of, acquired charac- 
ters, proposed originally by Lamarck but disputed by many inves- 
tigators; the difficulty in assuming that by selecting slight varia- 
tions a new species may eventually be produced, — it has been 
argued that no one has as yet succeeded in producing a new species 
artificially in this manner — and finally the causes of the variations 
which are taken advantage of in natural selection. 

Continuous Variations. Foremost among the scientists, who, 
following Darwin's lead, have applied the experimental method to 
the study of evolution, is Hugo DeVries, director of the botanical 
garden at Amsterdam, Holland. His carefully conducted experi- 
ments started with the seeds of "pure" strains, that is, unmixed 
with any other variety and therefore pure with reference to a 



CHAPTER XV. — MUTATIONS. 437 

selected character, and extended over a score of years and as many 
generations, each generation being self-pollinated and thus kept 
pure. The plants of each generation were painstakingly studied, 
photographed and represented by herbarium specimens so as to 
permit of accurate comparisons. DeVries' results demonstrated 
the existence of two distinct types of variations, the continuous and 
the discontinuous. Continuous variation is the usual kind and 
comprises fluctuations in such characters as size, form, color of the 
flowers, etc. Thus some of the flowers of a certain species will be 
a lighter blue and some a darker blue than the average; some of 
the plants will be taller and some will be shorter; some of the 
fruits will contain more and some fewer seeds than the normal 
number. But these fluctuations are kept within narrow limits. 
The average for each generation remains practically constant. 
Thus the wider variations from the average are few and the 
smaller departures relatively numerous. Changes in the ecological 
factors, such as light, water supply, temperature and soil constitu- 
ents, as well as the freedom from competition which cultivation 
assures, are chiefly responsible for continuous variations. It has 
been demonstrated repeatedly that these variations are not trans- 
mitted to the succeeding generations. Thus in a pure strain of 
beans, the largest seeds were selected for sowing and the resulting 
plants were kept pure by self-fertilization. This was carried on 
through several generations but no increase in the average size of 
the seeds was obtained. Again, though it is well known that the 
yield of sugar by sugar-beets has been increased through selecting 
seed from plants of high sugar content, this advantage is lost as 
soon as the selection of seed is neglected. 

Mutations. Discontinuous variations are those which arise sud- 
denly and result in the formation of new characters, which are 
then capable of transmission. DeVries was the first to demon- 
strate their importance and to advance the theory that natural 
selection depended upon them rather than on continuous variations. 
DeVries termed discontinuous variations mutations and the plants 
which give rise to them mutants. Such plants are said to be mutate. 
Thus it is believed that the common cabbage, kohlrabi, cauliflower 
and brussels sprouts are mutants or "sports" of the same plant, 
the wild cliff-cabbage. Thornless cacti, beardless oats and green 
roses are other instances of mutants. "Bud sports" such as nec- 
tarines and seedless oranges have resulted from the mutation of 
buds. DeVries made the remarkable discovery that a group of 



438 PART IV. — TAXONOMY. 

plants of Lamarck's Evening Primrose (Enothera Lamarckiana) 
growing in an abandoned potato field near Amsterdam were evi- 
dently in mutating condition. Associated with them, he found 
later two new forms which he judged had grown from them as 
mutants. From sowings of the seeds of normal plants, pedigreed 
through a series of generations, DeVries obtained several new 
forms which bred true and proved to be true mutants. These 
differed so widely from the parent form as to be entitled to rank 
as different species. Mutations, unlike continuous variations, are 
not due directly to variations in environment, although these may 
have an influence upon mutation. Apparently they are due to 
fundamental changes arising in the gametes. 



CHAPTER XVI.— HEREDITY. 

SIGNIFICANCE. — MENDELISM. — LAW OF DOMINANCE. — UNIT CHARAC- 
TERS. — PURITY OF GAMETES. 

Heredity may be defined as the transmission of characters or 
qualities from parent to offspring. It includes the resemblances 
of the individual to its ancestors, as contrasted with the variations 
by which individuality is expressed. Though the inheritance is 
constant, so that the characters of a species are faithfully repro- 
duced with but little change from generation to generation, yet 
these resemblances are not expressed in every detail in each indi- 
vidual, and, with plants no less than with animals, two individuals, 
however closely related, are never exactly alike. 

In the lower or unicellular forms of plants, where reproduction 
consists of simple cell-division, and the parent cell dividing forms 
two daughter cells which then separate and become distinct indi- 
viduals, the offspring are merely segments of the parent, the latter 
terminating its existence as an individual, with the appearance 
of its offspring. In such instances the inheritance is clearly 
carried by the protoplasm or living material which has passed 
from the parental cell into the offspring. But in the higher plants, 
as we have seen (Reproduction, page 108), only the protoplasm 
of sperm and the egg are transmitted to the offspring, hence these 
sex cells or germ cells must bear all the heritable characters. In- 
deed some biologists hold that this germ plasm is of nature differ- 
ent from the protoplasm of the other living cells of the plant and 
they distinguish accordingly between the "germ plasm," derived from 
the sex cells and the organs immediately involved in their produc- 



CHAPTER XVI. — HEREDITY. — MENDELISM. 439 

tion, and the "somatoplasm" or body plasm which comprises the 
protoplasm of the vegetative parts. It is held that changes in the 
somatoplasm may result from altered environment and such 
changes may bring about modifications in the vegetative organs 
of the plant but do not affect the germ plasm and therefore are 
not heritable. The germ plasm, on the other hand, is continuous 
from one generation to the next and the only changes experienced 
by it are due to mutations such as those already described. In 
vegetative reproduction the somatoplasm only is involved, but here 
the offspring is simply an isolated part of the parent plant which 
has become separated and now leads an independent existence. 

Mendelism. The experimental studies of Gregor Mendel, an 
Austrian monk, are among the most important biological investi- 
gations ever made. He selected common garden peas as meeting 
best the requirements for his experiments. These plants afford 
varieties exhibiting well-marked differences which are constant, or 
"breed true," from generation to generation. They are self-ferti- 
lized and hence of pure strain, that is, without hybrid characters. 
The plants are easily cultivated, easily protected against the influ- 
ence of foreign pollen and rapidly complete their life cycle from 
germination to the production of seed. Some of the varietal char- 
acters chosen for observation by Mendel were: 

Difference in size, i.e. tallness as contrasted with dwarfness. 

Difference in the shape of the ripe seeds, i.e. round and smooth 
seeds as contrasted with angular and wrinkled seeds. 

Difference in color of the cotyledons, i.e. a shade of yellow- 
orange as contrasted with a shade of green. 

Other differences noted by him were in the color of the seed 
coat, the form and color of the ripe pods and the location of the 
flowers on the stem. Mendel's efforts were directed toward cross- 
fertilizing selected varieties, each showing one or more of the 
above-mentioned characters, and watching the behavior of the 
resulting hybrids for several generations so as to determine the 
recurrence of the parental characters in the offspring. Since the 
garden pea is normally self-fertilized, it was necessary to remove 
the stamens from the selected flowers before the pollen was shed 
and to artificially cross-pollinate them by bringing pollen from 
the other plant selected as a parent. Then the flowers were pro- 
tected from foreign pollen by tying paper bags over them. 

Mendel crossed varieties, differing in one or more of the prom- 
inent characters mentioned above and then carefully bred the 



440 PART IV. TAXONOMY. 

hybrids for several generations by self-fertilization and recorded 
his results. 

He found that pairs of contrasting characters were exhibited 
by the progeny in the same general way and that it made no differ- 
1 ence whether the selected character came from the staminate or 
from the pistillate parent. Thus in experimenting with peas 
showing in one parent the character of tallness and in the other 
parent the character of dwarfness, Mendel found that the first 
generation of offspring, which he termed the Fi generation, all 
exhibited tallness. But in the second or F 2 generation, obtained 
from self-fertilized plants of the first generation, some were tall 
and some were dwarf in the proportion of three tall to one dwarf 
plant. In the third or F 3 generation, all the dwarf plants bred 
true, that is, produced only dwarfs, while only one-third of the tall 
plants bred true for tallness and the remainder behaved as the F, 
generation, producing two-thirds tall and one-third dwarf plants. 
Succeeding generations acted like the F 3 . Mendel termed the pre- 
dominating factor, i.e. tallness, a dominant, and the contrasting 
character, i.e. dwarfness, a recessive. Evidently then, in the F 3 
generation, one-fourth of the plants (the pure dwarfs) carry 
only the recessive factor, one fourth (the pure tails) only the 
dominant, and one-half (the impure tails) carry both factors, but 
exhibit only the dominant. 

The pure tails, the impure tails and the pure dwarfs are pro- 
duced in the F 2 generation in the ratio of 1:2:1 and the impure 
tails always produce these three kinds in the same ratio, 1:2:1, 
or, counting the pure tails and the impure tails together, for there 
is no apparent difference in the plants themselves but only in the 
offspring, we get the ratio: 3:1, as first observed. When both 
factors, for tallness and for dwarfness, are present, the dominant 
character only appears. Therefore, all the plants of the Fi genera- 
tion are tall, and so are all the impure dominants of the succeed- 
ing generation, as indicated in the following diagram. (Fig. 616.) 

The ratio 1:2:1 recalls the algebraic expression of the square 
of a+6, namely, a 2 +2ab+b 2 , assuming that a and b each equal 1. 
In plants (T+d) X (T+d)=TT+2Td+dd, in which T represents 
the dominant, tallness, and d the recessive, dwarfness. 

Law of Dominance. As a result of many similar experiments 
Mendel formulated the Law of Dominance, as follows: "When 
pairs of contrasting characters are combined in a cross, one char- 



CHAPTER XVI. — PURITY OF GAMETES. 441 

acter behaves as a dominant over the other, which is a recessive." 
Such pairs of contrasting characters are known as allelo7norphs. 
Unit Characters. Mendel held that such characters as tallness, 
dwarfness, wrinkled seeds, yellow cotyledons, etc., are inherited 
as independent units and are not affected by other characters or 

T < ■ > d [Parents] 

\i [Fj 

T XTT^mtTd ~t3~1 d [F s ] 

Fig. 616. — Diagram illustrating the inheritance of a dominant character 
(tallness) indicated by T. and a recessive character (dwarfness) indicated by d. in 
the first, second and third hybrid generation. 

units. Thus hybrids from a tall and a dwarf parent will behave 
the same in regard to tallness and dwarfness unaffected by other 
characters such as wrinkled seeds or yellow cotyledons. 

Purity of Gametes. Basing his theory upon his conception of 
unit characters, Mendel argued that a gamete can contain but one 
of the two allelomorphs, that is, a gamete may bear the gene or 
unit character for tallness but not the gene for dwarfness, 
although it may, of course, bear other genes, such as those for 
wrinkled seed and yellow cotyledons. The hybrid plant of the 
first generation bears both of the allelomorphs or contrasting unit 
characters derived from its parents, but when this hybrid produces 
gametes, each gamete bears but one of the allelomorphs. This was 
Mendel's theses concerning the segregation and purity of gametes. 
It is confirmed by the observation that pure dwarf and pure tall 
plants of the second generation and succeeding generations breed 
true and have evidently no genes for the contrasting characters. 
The production of the hybrid of the first generation results from 
the fertilization of the egg cell derived from one parent by the 
sperm cell from the other parent. If one parent bears the dom- 
inant and the other the recessive allelomorph, the hybrid will have 



442 



PART IV. — TAXONOMY. 



both and will be heterozygous. If, on the other hand, each parent 
bears the same gene or unit character, the offspring will bear a 
"double dose" of this unit character and none of its contrapVinp 




F Hybrid 



Dwarf Parent 



Gametes 



Fig. 617. — Diagram illustrating behavior of chromosomes in Mendel's cross 
of tall and dwarf peas. Large rectangular figures, nuclei of zygotes or mature 
individuals ; large circles, gametes ; small circles within zygotes and gametes, 
chromosomes; letters on chromosomes, determiners (T, tallness ; D, dwarfness). 
From Coulter & Coulter, Plant Genetics. 

character and will therefore be homozygous. Homozygous plants, 
when self -fertilized, breed true or are pure for a certain unit-char- 
acter; their gametes, therefore, must be alike in respect to it. 





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Fig. 618. — Diagram illustrating the behavior of the first hybrid generation 
(Fi) when inbred. Illustrates the meaning of "segregation" and "purity of 
gametes" and how chance matings of Fi gametes result in 3:1 ratio in F2 gen- 
eration ; dwarf individual produced only by zygote in lower right-hand corner. 
From Coulter & Coulter, Plant Genetics. 



But the gametes of heterozygous plants, in equal proportions, will 
bear one or the other but never both of the contrasting characters, 
and their descendants will be equally divided between heterozygous 



CHAPTER XVI. — PURITY OF GAMETES. 



443 



and homozygous kinds. Mendel's keen observations and deductions 
concerning the purity of gametes have been borne out by the later 
study of the mechanism of cell division, in which it has been deter- 
mined that each chromosome of the parent cell divides into two 
equal parts and each daughter cell receives one of these parts. It 
seems fairly certain that the chromosomes bear the heritable char- 




© ® 
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F, Hybrid 



Dwarf Wrinkled 
Parent 



Gametes 






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®© 



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©© 



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© 2 © 

©® 



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Fig. 619. — Diagram illustrating dihybrid ratio. Upper part shows how orig- 
inal parents were crossed to give Fi hybrid; lower part shows Fi hybrid pro- 
ducing four kinds of gametes ; chance matings among these gametes, when Fi is 
inbred result as indicated in the large set of squares and explains the 9:3:3:1 
ratio in the F2 generation. Four phenotypes result in the F2 generation, namely : 
nine tall, smooth individuals (squares numbered 1, 2, 3, 4, 5, 7, 9, 10, 13) ; three 
dwarf smooth (11, 12, 15); three tall wrinkled (6, 8, 14); and one dwarf 
wrinkled (16). There are four homozvgotes (1, 6. 11, 16); the remainder arc 
heterozygotes. (From Coulter and Coulter, Plant Genetics.) 



444 PART IV. — TAXONOMY. 

acters. When the gametes are produced, reduction division occurs 
and each gamete receives but one-half of the chromosomes of the 
individual that produced it. (See page 171.) 

The term phenotype has been applied to plants or animals 
which are alike, whether heterozygous or homozygous, while the 
term genotype implies organisms that have similar germinal con- 
stitution. The Mendelian ratio in the second hybrid generation is 
1:2:1 if based on genotypes, but 3:1 if based on phenotypes. It 
will be recalled that there are only two phenotypes, viz., tall and 
dwarf, but there are three genotypes, viz., pure tall, impure tall 
and pure dwarf. 

So far we have considered but one pair of allelomorphs, select- 
ing tallness and dwarfness. Many such contrasting characters 
have been observed and can be treated in similar manner. Thus, 
selecting a tall variety with smooth seed for one parent and cross- 
ing with a dwarf variety with wrinkled seed, we have two pairs 
of allelomorphs to consider. Representing the dominant characters 
by the capital letters T for tallness and S for smoothness of seed, 
and the recessive characters by small letters, d for dwarfness and 
w for wrinkled seed, we will have the algebraic formula (T+d) X 
(T+d)=TT+2Td+dd, and similarly (S+w) X(S+w)=SS+2Sw 
+ww, and combining these we have TTSS+2SSTd+SSdd+2TTSw 
+4TdSw+2Swdd+TTww-f 2Tdww+ddww. This gives us sixteen 
individuals, including nine genotypes and four phenotypes, the 
latter including nine tall smooth individuals, three smooth dwarfs, 
three tall wrinkled and one dwarf wrinkled, or a 9:3:3:1 ratio. 
It will also be observed that only four of these individuals are 
homozygous and will therefore breed true, while the remaining 
twelve are heterozygous. (See Fig. 619.) This illustrates a 
dihybrid ratio as compared with the monohybrid ratio earlier con- 
sidered. Trihybrid ratios involve three pairs of contrasting char- 
acters and produce eight phenotypes in sixty-four individuals. 
Higher and more complex ratios are possible, for a limit would 
seem to be established only by the number of chromosomes in the 
cells of the plant. 



CHAPTER XVII. — ECOLOGY. 445 

CHAPTER XVII.— ECOLOGY. 



SCOPE. ECOLOGICAL FACTORS. PLANT SOCIETIES. — PLANT GEOGRAPHY. 

IMPORTANCE OF ECOLOGY. 

Scope of Ecology. In the preceding chapters, the classification 
of plants based on their relationship has been considered. By the 
relationship of plants is understood their phylogeny or their 
genealogy, in other words relationship based on lines of descent. 
Such relationship is most clearly indicated by the reproductive 
organs of the plant. Hence, in assigning the place of the higher 
plants in taxonomic arrangements, their flowers are chiefly consid- 
ered. But frequent mention, throughout our text, has also been 
made of the habits of plants, that is, whether certain plants are 
parasites, saprophytes or independent plants, and whether they are 
climbers, epiphytes, aquatic plants, etc. It has been noted that 
these habits affect chiefly the vegetative organs of the plant. It is 
a matter of common observation that certain plants may resemble 
each other in habit {e.g. Wild Grape and Moonseed vines) and yet 
be very distantly related. Also that plants of similar habits may 
occur in similar places or surroundings, known as their habitat. 
Attention has been called to the fact that plants must compete 
successfully with other plants and with animals, and must survive 
unfavorable conditions of their environment, such as light and 
shade, heat and cold, moisture and drought. Only those plants that 
can successfully adjust themselves to these factors of their environ- 
ment are able to flourish and to extend their habitat. It is the 
province of Plant Ecology to study the adjustments of plants to 
their surroundings as well as the distribution of plants in relation 
thereto. It may again be pointed out that phylogenetic relation- 
ship may have little bearing on ecology; especially is this true of 
the higher plants (Spermatophytes). Thus it may happen that a 
tree (the Elm), a vine (the Hop) and an herb (the Nettle), though 
differing widely in habit, are members of the same order (Urti- 
cales) of the phylogenetic classification. In the lower groups the 
connection is more evident; thus the Fungi show remarkable uni- 
formity in their parasitic or saprophytic habits; practically all the 
Algae are water plants; the Mosses are chiefly carpet plants in 
moist locations, and most of the Ferns are shade-loving. 

Some of the problems of plant ecology are: 



446 PART IV. — TAXONOMY. 

To learn what species of plants are associated together in sim- 
ilar locations. 

To determine why these species congregate to form plant asso- 
ciations. 

To define the special habit and habitat of each species. 

To study the relations of plants to their environment; how 
they adjust themselves to light, shade, water supply, warmth, cold, 
various kinds of soil, influence of winds, competition with other 
plants and activities of animals. 

To investigate the causes of variation in the structure of plants, 
as affected by these environmental factors and to arrive at the 
meaning of the forms of plant organs. 

One phase of ecology deals with plants as individuals, with their 
individual structures, forms and adaptations, and has been con- 
sidered sufficiently for our purpose in connection with morphology 
in Parts I and II of this book. As an instance of the bearing of 
ecology upon morphology, it may be pointed out that the subject 
of pollination (Part I, Chapter XII) is largely an ecological one, 
since it is so closely involved with the adaptations of flowers to 
secure cross-pollination and especially to make sure of the visits 
of insects. 

Another phase of ecology deals with plants grouped into socie- 
ties or associations, and will be briefly considered here. 

Ecological Factors. The external factors which affect the struc- 
ture of the plant, and determine its habitat, include light, heat, 
water, soil, wind, other plants and animals. It is to these factors 
that the plant must successfully adjust itself in order to survive. 

Light. The importance of light in the photosynthetic processes 
of the plant has already been discussed. (Part III, Chapters III 
and IV.) So essential is light to the life of the plant, that its 
intensity and duration play a most important part in the distribu- 
tion of plants and determine the range of the various species. The 
effects of light on growth forms, the production of weak and 
spindly shoots due to insufficient light, and the phenomena of etio- 
lation have already been mentioned. It has been often observed 
that the light needs of different species vary. Some are especially 
suited to shade, others flourish only in full sunlight. The efforts 
of plants to climb, and the development of tall stems are endeavors 
to secure sufficient light. The fact that individuals growing in 
shade develop larger leaves than others of the same species grow- 
ing in sunshine is a form of adjustment to secure the optimum 



CHAPTER XVII. — ECOLOGICAL FACTORS. 



447 



amount of light. The full, rounded form of maples or oaks grow- 
ing in the open, as contrasted with tall, slender and crowned forms 
of the same tree when growing in forests, is another instance of 
light effect. 

The structure of the leaves of shade-loving and sun-loving 
plants is also different. The latter are often isolateral or centric 
or if dorsiventral they have a thickened cuticle, protected stomata 
(Fig. 620) and may have water storage tissue above the chloren- 




Fig. 620. — Epidermis of the leaf of Cycas revoluta, illustrating the protec- 
tion of the stoma by a "vestibule." Above — Transverse section partly in per- 
spective ; A, ordinary epidermal cell ; B, vestibular cell ; C, collar cells support- 
ing the vestibule ; D, guard cells of the stoma. Below, at left. — Tangential sec- 
tion at C D in upper figure. Below, at right. — Tangential section at 

A B in upper figure. Cells of the vestibule cut through near their base. 



chyma, while the shade-loving plants bear thin, soft leaves, dorsi- 
ventral in structure, deep green in color and usually little divided. 
Heat. One of the most important ecological factors is heat. 
Its effects on growth have already been indicated (Part III, Chap- 
ter III). It is well known that the range of each species is deter 



448 PART IV. TAXONOMY. 

mined by climatic conditions. Thus, owing to its susceptibility to 
frost, the Orange is limited to warm climates, while Oats and Bar- 
ley do best in colder climates. Similarly, the zones of temperature, 
arctic, temperate and tropical, are also distinguished by their 
characteristic flora. Extreme cold and extreme heat are alike 
fatal to plant life, hence the ice-bound polar regions and the hot 
deserts in the tropics are characterized by sparseness of vegeta- 
tion, though there is scarcely a spot to be found where plants are 
entirely absent. The succession of flowering plants so familiar to 
us, as summer succeeds spring and is followed by autumn, is like- 
wise an evidence of the importance of the heat factor. Protection 
of plants against extremes of heat and cold have already been 
mentioned; the prostrate forms of arctic plants and the formation 
of rosettes by the basal leaves are examples of the latter, while 
certain resistant properties of the protoplasts which are probably 
due to changes in the condition of the protoplasm itself, explain 
the immunity to cold of such unicellular plants as the Snow Alga 
(Sphaerella) . 

Water. The absolute necessity of water for maintaining life 
has already been discussed (Part III, Chapter II). The adjust- 
ment to water needs varies with different plants, from those that 
live completely submerged in water to those that are able to with- 
stand the severe drought of deserts. No other ecological factor 
makes so marked an impression on the structure of the plant as 
the water supply. As with light and heat, so there is a minimum, 
optimum and maximum amount of water that each species can 
use, and an excess of water, as well as a deficiency, may be fatal. 
A moist climate is on the whole favorable to a longer life for indi- 
vidual plants while dry climates shorten the vegetative period, 
produce earlier flowering and fruiting and favor the development 
of annuals or perennials with a marked resting period. More 
irregular in its distribution than heat and not less necessary to 
the vital processes of the plant, water takes the first place in the 
factors which determine the distribution and character of plant 
associations. 

Soil. The nature of the soil, both in regard to its chemical 
constituents, its physical structure, its air content and especially 
the amount of water contained in it, is of great importance as a 
factor in determining the kinds of plants that may grow in any 
given location. Among the commonly recognized kinds of soil are 
rock soil, sand soil, clay soil, humus and loam. 



CHAPTER XVII. — ECOLOGICAL FACTORS. 449 

Sand soil is composed chiefly of particles of quartz, but felspar, 
mica and volcanic products may be present. Sandy soil is loose, 
and is readily permeated by air and water, but retains water only 
slightly. It dries quickly and becomes rapidly heated by sunlight 
but cools with equal rapidity at night, hence may show wide 
ranges of temperature. 

Clay soil, chiefly composed of invisible particles of kaolin — 
hydrated silicate of aluminum — exhibits to a high degree the power 
of absorbing water. It swells and becomes plastic when moist, but 
dries to a stony hardness and cracks with drought. It is sticky 
or "heavy," admits air but poorly and as a subsoil, is almost imper- 
meable to water. 

Humus soil is rich in decaying vegetable matter, often with 
some animal matter, and is black or brown in color. It contains 
much carbon, and may contain nitrogen. Peat, a bog soil, consists 
wholly of humus in which the vegetable material is only partly 
decayed. Of all soils, peat has the greatest capacity for holding 
water and, since air is virtually excluded, humus acids develop 
which have an injurious effect on vegetation. Muck is a black 
soil containing an excessive amount of humus. Loam, the best of 
garden soils, is an intimate mixture of humus with sand and clay. 
It rarely contains more than ten per cent of organic matter, is 
neutral or alkaline in reaction and affords a home for earthworms, 
insects, fungi, etc. 

The amount of water present in the soil is of first importance, 
when we recall that plants ordinarily secure their water supply 
entirely through their roots. Since the water in soils is held in 
the form of films surrounding the soil particles, it is evident that 
a soil constituted of very fine particles (clay) will retain water 
more tenaciously than one composed of coarse particles (sand). 

Of scarcely less importance to plants is the presence of air in 
the soil, for the root cells like other living organisms must respire, 
and for respiration oxygen is essential. Air ordinarily fills the 
larger spaces in soils, spaces not occupied by the water films, and 
is more or less in connection with the atmosphere. When the air 
becomes charged with carbon dioxide, as a result of respiration, it 
needs to be replaced, hence the value to crops of moderately heavy 
rains, with intervening periods of dry weather. 

Mineral salts dissolved in the soil water, though needed in but 
small amount, are necessary to the welfare of plants. Such salts 
when supplied artificially are known as "fertilizers." They are 



450 PART IV. — TAXONOMY. 

especially compounds containing nitrogen, phosphorus, potassium, 
calcium, sulphur and magnesium. In nature, they result in part 
from the disintegration of rocks and in part from the action of 
living organisms. 

Wind. While wind is of value to plants in carrying pollen and 
aiding in the distribution of seed, yet it may also have an injurious 
effect in excessively increasing transpiration and in carrying the 
spores of disease-producing fungi. It also dries the soil and, in 
cold weather, when the activity of the root is but slight, shoots 
and branches are killed and deformities of growth are caused. 
Particularly are the trunks of trees bent and the branches curved 
away from the windward side, in exposed situations where high 
winds prevail. 

Other Plants and Animals. Competition among different spe- 
cies of plants is a factor in their distribution. A familiar example 
is that crop plants do poorly under the shade of trees and that 
"weeds" crowd out garden plants. Many species have spread, as 
weeds, far from their homes. Thus Datura stramonium, a native 
of Asia, has spread as a common weed through this country, and 
Salsoli kali, the so-called "Russian Thistle," a plant of the Euro- 
pean seacoast, has become a pest in the wheat fields of our North- 
west. We have contributed to the weed list our Waterweed (Elodea 
canadensis) which now is common in Central Europe, as also is our 
Canada Fleabane (Erigeron canadensis). Leguminous plants are 
often helpful neighbors, since their root tubercles afford a home 
for nitrogen-fixing bacteria, but Bindweeds and Morning Glories, 
in climbing, break down plants or interfere with their light. On 
the other hand, plants from many different habitats do well under 
conditions of cultivation, largely because competition has been 
removed. 

The importance of insects in cross-pollination has already been 
considered as well as the service of larger animals in aiding in the 
distribution of seeds. In addition to the foregoing general ecologic 
factors, there are others of lesser importance in the distribution of 
plants, such as the influence of the living vegetable covering on 
the soil and the influence of the non-living covering, such as snow. 
It is also to be borne in mind that factors act together and not 
singly and that definite relations exist between the factors them- 
selves. Thus light and heat are interdependent; air movements 
affect water needs by increasing transpiration, and cold acts to 
lessen absorption of water from the soil, producing a physiological 



CHAPTER XVII. — PLANT SOCIETIES. 451 

drought. According to their adjustments to these factors of envi- 
ronment, plants are classified into ecologic groups or societies. 

PLANT SOCIETIES. 

Water Plants. These include the so-called Hydrophytes, both 
those that float free and those that are attached by roots or hold- 
fasts. 

Among the free-swimming forms are the Flagellata, the Peri- 
dinas and the motile spores of the Algae. The floating forms 
include the Desmids and Diatoms and the non-motile spores of 
Algae and Fungi. Such microscopic hydrophytes constitute the 
so-called "phyto-plankton," the ultimate source of food for marine 
animals and often so abundant as to impart a distinctive blue, 
blue-green or yellow-green color to the water. Other Algae, orig- 
inally attached, but afterward breaking loose, float as "drifting 
seaweeds" and continue to propagate vegetatively. The Sargasso 
Sea, characterized by Sargassum in great abundance, is of this 
nature. Included in the attached hydrophytes are many Cyano- 
phycese, Chlorophycex and Rhodophycese. Here also are the Rock- 
weeds of our seacoasts and the giant Kelps, so abundant as to be 
harvested as a source of potash and iodine. A few alga-like Sper- 
matophytes such as Elodea canadensis and Vallisneria spiralis as 
well as the curious Bladderwort (Utricularia) have a similar 
habitat. 

The peculiar conditions surrounding submerged water plants 
produce a structure that is characteristic. The necessary gases 
(oxygen and carbon dioxide) required by all green plants are 
accessible only through the water, in which relatively small pro- 
portions are dissolved. This applies also to the mineral salts. 
Much-divided leaves and stems with a thin epidermis destitute of 
water-proof cuticle favor the absorption of these constituents, and 
since all parts of the plant are in contact with water and can 
absorb, water-conducting tissue is scarcely needed. The buoyancy 
afforded by the water lessens the need of mechanical strength and 
support. Submerged water plants, therefore, as a rule collapse 
when taken from the water. Anchored forms which are subject 
to tidal or wave action may have quite a tough structure. 

Marsh Plants, such as the Water Lilies, whose leaves float on 
water but which are attached to submerged rootstocks, differ in 
habit and structure from the preceding, inasmuch as their supply 



452 PART IV. — TAXONOMY. 

of carbon dioxide and oxygen is drawn chiefly from the atmosphere 
and only a relatively small part from the water solution. Such 
plants are Aerophytes rather than Hydrophytes, physiologically. 
In the Water Lilies the petioles are long and flexible so as to be 
capable of adjustment to the depth of the water and are provided 
with large air passages whereby gases secured from the air by the 
leaf are supplied to the submerged parts. In these plants the 
leaves are commonly rounded in form, flat, and the upper surface 
of the leaf sheds water remarkably. In those tiny floating plants, 
the Duckweeds, the roots, hanging free in the water, prevent the 
leaves from upsetting. 

Swamp societies, comprising Sedges, Rushes, Reeds, Bulrushes, 
Cat-tails and other plants whose leaves are borne above the surface 
of the water, are related to the hydrophytes in habit. Associated 
with those and forming a fringe along the borders of the swamp 
societies may be found a few trees, notably Alders and Willows. 

In bog swamps, certain mosses (Sphagnum) spread as a float- 
ing mass which afterwards condenses, forming Peat, upon the 
surface of which the living mosses are borne. 

Normal Plants, or Mesophytes, are those forming the common 
vegetation. They are suited for ordinary conditions of plant life; 
a moderate amount of water, fertile soil and free access of air. 
Hence when swamps are drained or as they gradually fill up owing 
to the decaying vegetation or other causes, the hydrophytic swamp 
societies gradually change to the mesophytic forms. These corre- 
spond to the plants which we have chiefly discussed in the fore- 
going parts of this book. They are provided with roots for absorp- 
tion of water and soil solutions as well as for fixing the plant in 
place, green leaves for photosynthesis, and supporting stems. The 
above-ground parts, exposed to the drying influence of the air, are 
protected by a water-proof covering of epidermis or cork, through 
which openings for the passage of gases and water vapor are pro- 
vided by the stomata and lenticels. They have a well developed 
mechanical system capable of withstanding the strains caused by 
the wind and the weight of the leaves, flowers and fruit. 

Among the many mesophytic plant societies are : the deciduous 
forests, composed of our common deliquescent trees, such as 
Maples, Oaks, Elms and Beeches; meadows and prairies, in which 
grasses and herbs predominate and trees are few or entirely 
absent; thickets of shrubs and small trees, and rainy tropical for- 



CHAPTER XVII. PLANT SOCIETIES. 453 

ests, characterized by the abundance of trees, shrubs and vines, 
forming an almost impenetrable jungle. 

Desert Plants, or Xerophytes, are plants which are adapted to 
conditions of drought, that is, where air and soil are dry the 
greater part of the year. Xerophytes not only possess features 
which lessen transpiration, notably smaller leaf surface, sunken 
stomata, abundant trichomes, and thickened epidermis, but they 
also have devices for storing water (water storage tissue) and 
may also reach deep into the soil by means of long tap roots. In 
most xerophytic areas there is a short wet season during which 
most of the plant growth occurs. Immediately following this 
many of the herbs lose their foliage and survive only in their 
underground rhizomes or tubers. Annuals bridge over the dry 
season in the form of seeds. Among the xerophytic plant societies 
are: the evergreen forests, including such trees as Pines, Hem- 
locks, Spruces and Firs, whose adaptations to the physiological 
dryness of the long northern winters and to high altitudes also 
enable them to flourish in dry situations in temperate climates 
and even to survive mesophytic conditions; the xerophytic thickets, 
represented by the chayparal of our southwestern states; the 
desert societies, the extreme types of xerophytes, and including in 
our country the Cactus and Yucca; the rock societies, chiefly 
lichens and mosses growing on dry and exposed rocks; and the 
heaths of northern Europe, where, owing to the acid soil, the pre- 
dominant vegetation is Ericaceous shrubs. 

The Seacoast plants, or Halophytes, grow in habitats where, 
owing to the proximity of the salt water, there occurs an appre- 
ciable amount of salt in the soil. The presence of salt inhibits the 
absorption of water by the roots and as a result the plants growing 
in this soil possess the features of xerophytes. In fact many 
xerophytic grasses and annuals occur in such habitats, along with 
certain succulents such as Saltwort. 

Ecological Plant Geography. The connection between the topog- 
graphy of the country and its characteristic vegetation areas is 
obvious. Even a casual observer recognizes the distinctive plant 
formations of swamps, prairies, thickets and woods. A more 
careful inspection discloses that these plant formations contain at 
least several, and more often, many kinds of plants. Among such 
plants, the largest and best adapted forms will dominate and lend 
a distinctive character to the whole formation. Rarely there may 
be but one of these dominants but usually there are several. Thus 



454 PART IV. — TAXONOMY. 

in the flood plain forests of river "bottoms," Elms and Basswoods 
are the dominant trees; climbing upon these are the vines, Wild 
Grape, Greenbrier, Poison Ivy and Virginia Creeper; in the under- 
growth are the Haws {Cratxgus) and many others, while the 
spring-flowering herbs, Spring Beauty, Phlox, several Trilliums, 
Dogtooth Violet, Indian Turnip, the blue and the yellow Violets, 
Collinsia, etc., form the carpet. 

Where there are several dominants in a plant society these are 
sometimes spoken of as commensals (literally, eating at the same 
table) and the condition of shared dominance is termed commen- 
salism. This should be distinguished from the relationship between 
host and parasite, even when this is mutually beneficial (sym- 
biosis) . 

Plant associations are often designated by their dominant 
forms; the pine forest, the oak forest, the tamarack swamp and 
the peat bog are examples. 

The Succession of Plant Societies. Among plants, as among 
animals and men, there is sharp competition. With such nicety 
are the successful plants adjusted to their surroundings, that 
every change in the environmental factors puts them at a dis- 
advantage, and may favor a more fortunate competitor. Yet we 
know that everywhere and without ceasing, these changes go on. 
Climatic fluctuations, even though they be slight ; the occurrence of 
unusually wet or unusually dry seasons; the activities of man in 
cultivating fields, clearing forests or draining swamps ; the attacks 
of fungi and of insects; the gradual filling in of shallow lakes by 
decaying vegetable matter; the erosion caused by streams, as well 
as the formation of flood plains; the disintegration of rocks with 
the production of new soil; all of these profoundly affect the plant 
societies inhabiting the areas in which these changes occur. As 
swamps are filled, the hydrophytic societies are replaced by meso- 
phytic ones, while the sparse flora of the sand dunes is gradually 
enriched as the soil becomes fixed through the growth of vegetation 
until at length xerophytes such as Pines are established, to be suc- 
ceeded in turn by Oaks and other mesophytes. In general, where 
climatic conditions permit, the trend is toward the production 
of conditions suited to mesophytes, to whom both xerophytes and 
hydrophytes are slowly losing ground. 

Importance of Ecology as Related to Medicinal Plants. Ecology 
has a most important bearing upon the cultivation of medicinal 
plants, in respect to the variation in the amount of medicinally 



CHAPTER XVII. — PLANT SOCIETIES. 



455 



active constituents under different ecological conditions and at 
different periods of growth. Thus Cinchona, grown under glass 
in this climate, yields no alkaloid; Belladonna root is richest in 
alkaloid in the late summer, autumn or early spring; Belladonna 
leaves are apparently most active medicinally at the time of flower- 
ing. Not only the quality but also the quantity of the drug pro- 
duced may be markedly affected by ecological factors. Digitalis, 
under favorable environment in Oregon, has attained a height of 
twelve feet, and Ricinus, an annual herb in our northern states, 
becomes a tree in the tropics. Both the superior fragrance and 
the yield of Peppermint oil depend largely upon the moisture and 
other conditions of the soil upon which the plant is grown. 




INDEX. 



ABSORPTION of water and soil 

solutions 262 

Acanthacea? 43 1 

Acaulescent plants 24 

Aceraceae 426 

Acids, plant 151 

Achenium 116 

Achlya lignicola 344, 345 

Acotyledonous embryos 128 

.'Ecidomycetes 354 

JEcidiosporec 354 

.Ecidia 350 

Aerobic bacteria 306 

^Estivation 69 

iEthallia of Myxomycetes 302 

Agaricaceae 360 

Agaricus campestris 360, 361 

Agaricus muscarius 361 

Aggregate fruits 122 

Agricultural botanv 13 

Akene 116 

Albuminous seeds 126 

Alburnum 235 

Aleurone grains 144 

Algae 308 

Alkaloids 148 

Allelomorphs 441 

Allogamy 95 

Alternation of generations in Ferns 380 

Amaryllidaceae 415 

Ament 63 

Anacardiaceae 425 

Anaerobic bacteria ,306 

Anaesthetics, effects of on plants.. 290 

Andraeales 378 

Androecium 71, 82 

Androspores 324 

Anemophilous flowers 95 

Angiospermae, classification of 411 

" general characters of 408 
" reproduction in ... 410 
Animals as agents in the disper- 
sion of fruits 114 

Annular vessels 203 

Annulus of Agarics 361 

Annulus of Ferns 387 

Anonaceae 423 

Anther^ 84 

Antheridia of Green Alga? 315 

" of Ferns 380 

of Mosses 369 

Anthoceros 374 

Anthocerotales 373 

Anthophore 77 

Anthotaxy 60 

determinate 61, 64 

indeterminate 61 

mixed . 68 

Antipodal cells 107 

Antitoxins 308 

Apetalae 420 

Apocarpous pistils 89 

Apheliotropic plants 283 

Apocynaceae 429 



Apogamy 381 

Apospory 381 

Aquifoliaceae 425 

Apothecium of Lichens 365 

Araceae 415 

Arales 415 

Aralia, flower of 418 

Araliaceae 427 

Araucarias. flowers of 403 

Archegonia of Mosses 369 

Archegoniates 380 

Archichlamydeaa 420 

Aril 124 

Aristolochiales 421 

Aristolochiacene 421 

Ascent of water in plants 266 

Ascomycetes, general characters of 345 

Ascospores 341, 346 

Ascus 346 

Aspergillus 348 

Aspidium rhizome 225 

Ash of plants 260 

Assimilation 274 

Autogamy 95 

Auxospores 313 

BACILLUS 307 

Bacteria, classification of 306 

" general characters of. . . . 305 

Bacteriology 308 

Bacterium 307 

Balsaminacea? 426 

Balsams 151 

Bangia 336 

Bark 220 

" layers of 237. 239 

Basidia 353 

Basidiolichenes 368 

Basidiomycetes 353 

Basidiospores 340. 353 

Bast fibers 194 

Batrachospermum 336 

Beggiatoa 307 

Begoniaceae 426 

Berberidaceae 423 

Berry, definition of. . 118 

Biennials, definition of 16 

Bignoniaceae 431 

Bixaceae 426 

Bladder-wrack 334. 335,336 

Blue-green Algae ....*. 308 

Bog-mosses 376 

Boletus edulis • . . 361 

Bombaceae ' 426 

Boraginaceae 430 

Bordered pits in Pine Wood 199 

Botany, agricultural 13 

" definition of 13 

" floricultural 13 

" geographical 13 

" horticultural 13 

medical 13 

" paleontological 13 

pharmaceutical 13 



458 



INDEX. 



" structural 14 

" systematic 13 

Botrydiums 315 

Bracts 60 

Bractlets 60 

Branching, dichotomous 55 

monopodial 55 

" of or ans 55 

of roots 221 

Bromeliaceae 415 

Bromeliales 415 

Brown Sea-weeds 333 

Bryales 378 

Bryophyta, general characters of. . 368 

Budding of cells 173 

Bud scales 22 

Buds, kinds of. 21, 22, 23 

Buds, their nature 21 

Bulbs, structure of 29 

scaly 29 

" tunicated 29 

Burseraceae 425 

Butomus, floral diagram of 414 

Buxaceae 425 

CACTACEiE 426 

Caesalpinae 424 

Calcium oxalate 154 

Calycanthaceae 423 

Calyptra of Mosses 371 

Calyx .71, 76, 77 

Cambiform cells 205 

Cambium, fascicular 232 

Cambium, inter-fascicular 232 

Campanulales 431 

Campanulaceae 432 

Cannaceas 416 

Capillitium of Myxomycetes 302 

Capitulum, or head 63 

Capparidaceae 423 

Caprifoliaeea* ■ 431 

Capsule, definition of 119 

Capsules, dehiscence of 120 

Caricaceae 426 

Carpels 71 

Carpophore 77 

Carpospores of Red Alga?. ... 338, 340 

Caruncle 124 

Caryopsis 116 

Catkin 63 

Caulicle or hypocotyl '126 

Celastraceas 425 

Cell, definition of 132 

" typical, structure of 133 

Cells, conjugation of 327 

" division of 168 

" formation of 168 

" shapes of 160 

" size of 161 

Cellulose in the cell wall 162 

Cellulose as reserve material 274 

Cell-wall ? 134. 157 

cellulose in 162 

" chemical changes in 162 

" cutinization of 163 

" lignification of 162 

" markings of 159 

" mineral crystals in 163 

" mucilaginous changes in 163 

" stratification of 163 

" striation of 164 

Central cylinder or stele 217 

Centric leaf 245 

Cereals 414 

Cetraria islandica 367 



Chara 330, 331, 332 

Charales .328, 329 

Chlamydomonas 320 

Chlamydospores 357 

Chlorophyceae 315 

Chlorophyll, functions of 269 

Chloroplasts 137 

Chondrus crispus 337 

Chromatin 135 

Chromatophores 136 

Chromogenic bacteria 307 

Chromoplasts 137 

Chromosomes 169 

Chromosomes as bearers of herit- 
able characters 443 

Chytridiaceae . . 344 

Chytridium 346 

Ciliary motion 281 

Circumnutation 285 

Cistaceae 426 

Cladophvlla 30 

Cladothrix 307 

Classification, characters most im- 
portant in 297 

Classification of plants ". 294 

Clavariaceas 359 

Clavaria rugosa 361 

Claviceps purpurea 349, 350 

Clay soil 119 

Cleistothecium 348 

Clethraceae 428 

Climbine-plants 25 

Closed collateral bundles 226 

Close-fertilization 95 

Club-Mosses, general characters of 391 

Club-root of Cabbage 303 

Coccus 306 

Cochlea 119 

Coenobium 317, 321 

Coleochrete 325 

Collateral bundles _ 220, 226 

Collective or multiple fruits 122 

Collenchvrna 178 

Colleters 213 

Columella of Mosses 371,374 

Combretaceae 427 

Commelinaceas 415 

Commensals 454 

Commensalism 454 

Companion cells 205 

Comparative study, value of 294 

Composita?, floral diagram of 418 

Composite, general description of 432 

Concentric bundles 224 

Conferva 314 

Confervales 322 

Confervoid Algae _ 322 

Conidia of Fungi 340 

Coniferales, general characters of 402 
Coniferales, mode of reproduction 

in 403 

Conjugates 326 

Conjugating Algae 326 

Conjugation of cells 327 

Connective 86 

Constituents of plants 259 

Constructive metabolism 255 

Continuous variations 436 

Contortae 429 

Contractility of protoplasm 245 

Convolvulaceae 430 

Coriariaceas 425 

Corms, characteristics of 28 

Cornaceae 427 

Cork tissue 191 



INDEX. 



459 



Corolla 71. 76, 80 

Corollas, choripetalous, forms of. . 80 

" gamopetalous, forms of.. 80 

Corona 80 

Corymb 62 

Cosmarium botrytis 328, 329 

Cotyledons 126 

Crassulacea? 424 

Cremocarp 117 

Crenothrix 307 

Cross-fertilization 95 

" agencies of ... . 95 

Cruciferae 423 

Crustaceous Lichens 366 

Crystal fibers 156 

Crystal sand 155 

Crystals of calcium oxalate 155 

Crystalloids 144 

Cucurbitaceaj 432 

Culm 65 

Cup Fungi 351 

Cyanophyceae 308 

Cvathaceae 386 

Cyathus 361 

Cycadales, j eneral characters of 399 

Cycas, fructification of 400 

Cycle number 72 

Cyme 65 

Cyperaceie 414 

Cystocarp 338 

Cystoliths 156 

Cytology, definition of 13 

Cytoplasm 134 

DARWINISM 434, 436 

Dehiscence of capsules 120 

Desert plants, or xerophvtes 453 

Desmids 327 

Destructive metabolism 25 5 

Determinate anthotaxy 64 

Diapetalae 422 

Diapensiacea? 428 

Diatomaceous earth 313 

Diatomeae 312 

Dichogamy in flowers 97 

Dichotomous branching 55 

Diclinism in flowers 97 

Dicotyledons, classification of.... 420 

embryos of . . .127, 418 

flowers of 418 

general characters of 418 

leaves of 417 

number of species of 420 

roots of 417 

Dicotyledon-type of stem 231 

Differentiated Monocotvledons ... 415 

Diffusion 263 

Digestion in plants 274 

Dihybrid ratios 443 

Dinoflagellata 312 

Dioecious plants 97 

Diplococcus 306 

Dipsaeeas 431 

Discolichenes 368 

Discomycetes 349 

Disk ..... 76 

Diseases produced by Bacteria... 308 

Dispersion of fruits 113 

Distribution of reserve materials.. 273 

Division, indirect nuclear 168 

reduction 171 

Dominants and recessives 440 

Dominants in plant associations. . 454 

Dotted vessels 202 

Drupe 117 



Ducts 202, 203 

Duramen 235 

EBENACEiE 429 

Ebenales 429 

Ecology 445 

Ecological factors 446 

Ecological plant geography 453 

Economic Botany 13 

Ectoplasm 135 

Egg-apparatus 107 

Elaboration of food 268 

Elaaocarpaceae 426 

Elasagnaceaa 426 

Elaters of Bryophytes 371 

" " Equisetineae 389 

Embryo, acotyledonous 128 

" definition of 126 

" formation of 108 

parts of 126 

polycotyledonous 128 

" position of in seed 126 

Embryolo y 13 

Embryo-sac 106 

Embryo, germination of 127 

" kinds of 126 

" of Coniferae 405 

" of Dicotyledons 418 

of Monocotyledons .... 413 
Embryos of parasites, and sapro- 
phytes 418 

Empetracea? 425 

Empusa muscorum 342 

Endocarp 118, 249 

Endodermal tissue 190 

Endodermis 218, 223 

Endophytic algae 308 

Endophytic bacteria 340 

Endopleura 124. 249 

Endosperm 125. 250 

formation of 108 

Endospore of Mosses 372 

Endothia parasitica 348 

Entomophthoreae 342 

Entomophilous flowers 96 

Entomopthora spha?rosperma .... 342 

Enzymes 146 

Epacridaceae 428 

Epicalyx 79 

Epicarp 118, 249 

Epidermal tissue 180 

Epidermis of leaf 41, 241 

stem 222 

Epigeous germination 127 

Epiphytes, roots of 17 

Epiphytic fungi 340 

Equisetum arvense 390 

Equisetineae 388 

Ergot of Rye 349 

Ericales 428 

Ericaceae 428 

Erysipheae, or Perisporiales 348 

Erythroxylaceae 425 

Euglena 311 

Eumycetes, or True Fungi 341 

EuphorbiaceaB 425 

Eusporangiatae 382 

Evolution 432 

Exalbuminous seeds 126 

Exoasci 353 

Exobasidium vaccinii 354 

Exospore of Mosses 372 

FACULTATIVE anaerobes 306 

Facultative saprophytes 340 



460 



INDEX. 



Fagaceae 421 

Fagales 42 1 

Farinales 415 

Fats 143 

Fermentation produced by Bacteria 308 

Ferments 146 

Ferns, leaves of 382 

" general characters of 382 

stems of 224, 382 

Fertilization, effects of outside of 

ovary 110 

Fertilization of the ovule 94, 105 

Fertilizers 449 

Fibro-vascular bundles, collateral. 220 

Fibro-vascular bundles, concentric 224 

Fibro-vascular bundles, radial.... 218 

Fibro-vascular bundles of leaf.... 243 

Filament 84 

Filicales, general characters of... 384 

reproduction of 384 

Filicineae 382 

Fixation of nitrogen 272 

Fixed-oils 143 

Flagellata 311 

Floral organs, histology of 247 

Floral parts, absence of 74 

" " adnation of 76 

" " anteposition of ... . 74 

" " coalescence of .... 76 

" " multiplication of.... 74 

" " union of 75 

Floriculture 13 

Flowers, actinomorphic . 75 

" allogamous 95 

" anemophilous 95 

" apetalous 74 

" arrangement of on the 

stem 60 

" autogamous 95 

" complete 73 

" cycle numbers of 73 

" entomophilous 96 

" diclinous 97 

" dichogamous 97 

" hermaphrodite 73 

" heteromorphism in 101 

" irregular 75 

naked 74 

" nature of 60,246 

" neutral 74 

" parts of 71, 247 

" pistillate 74 

" prefloration of 69 

" proterandrous 97 

" proterogynotis 99 

" regular 73 

" staminate 74 

" structure of 71 

" symmetrical 73 

' : typical 72 

" use of color in 96 

" use of nectar in 96 

" use of perfume in 96 

*' why interesting to bot- 
anist . : 58 

" zygomorphic 74 

Food, elaboration of 268 

Food of plants 261 

Foliaceous Lichens 366 

Follicle 119 

Forestry 13 

Fovilla 86 

Free cell formation 172 

Fructification of Lichens 365 

Fruits Ill, 249 



" changes in development of. Ill 

classification of 115 

" definition of Ill 

" dispersion of 113 

" structure of Ill 

Fruticose Lichens 366 

Fucales, or Rockweeds 334 

Fucus vesiculosus 334, 336 

Fumariaceae , 423 

Funaria hygrometrica 371 

Fungi, general characteristics of. . 339 

GAMETE, female 107 

Gamete, male 105 

Gametophyte, female 107 

Gametophyte, male 105 

Gamopetalae 427 

Gamopetalous corolla 80 

Gamosepalous calyx 77 

Gases in the plant 260, 267 

Gasterolichenes 368 

Gasteromycetes 257 

Geaster 361 

Gemma? of Mosses 375 

Gemmation of cells 173 

Genes, or unit characters 442 

Gentianaceae 429 

Gentianales 429 

Genotypes 444 

Geographical botany • 13 

Geotropism 282 

Geraniaceas . . .' 425 

Geraniales , 425 

Germ-plasm 438 

Gesneriaceae 431 

Glandular hairs 212 

Glans, or nut 117 

Globoids 144 

Globulariaceae 431 

Gloeocapsa 309 

Glomerule 65 

Glucosides 148 

Glumales 414 

Glumiflorae 414 

Gnetales, general characters of. . . 407 

Gonidia of Lichens 365 

Gonophore 77 

GramineaB 414 

Grasses 412, 414 

Green Algae 315 

Green-felts 316 

Growing points (meristems) 277 

Growth, defined . . .' 277 

" definite annual 23 

" grand period of 278 

" indefinite annual 23 

" influence of temperature 

on 278 

" influence of light on 279 

" phases of 277 

Gums 143 

Gum -resins , 151 

Guttiferas 426 

Gymnospermae, flowers of 398 

general characters 

of 398 

" orders of 399 

" stems of 240 

Gymnosporangium 356 

Gynaecium 71 

Gynandrous stamens 83 

Gynophore 77 

HABENARIA CILIARIS, flower 

of 103. 104 



INDEX. 



461 



Habitats of plants 445 

Hadrome 218 

Hairs, structure of 187 

Haloragidacete 427 

Halophytes, or seacoast plants. . . 442 

Hamanielidaceac 424 

Haustoria 340 

Head-cell of Chara 332 

Head, or capitulum 63 

Heart-wood 235 

Heat, as an ecological factor.... 447 

Heliotropism 283 

Heliobales 413 

Helvellales 351 

Hepatic* 372 

Heredity 438 

Hesperidium 118 

Heterocontae 314 

Heterocysts 309 

Heteromerous Lichens 365 

Heteromorphism of Flowers 101 

Heterosporous Pteridophyta 382 

Heterozygous parents 442 

Hip fruits 122 

Hippocastanaceae 426 

Histology 13, 14, 131 

Histology of floral organs 247 

" leaf 243 

" " leaf 241 

" roots 218 

" sterns 222 

Homoiomerous Lichens 365, 366 

Hormogones 310 

Homosporous ferns 382 

Homozygous parents 442 

Horsetails 388 

Horticulture 13 

Host plant 340 

Humus soil 449 

Hybrids, behavior of 441 

Hydatodes, or water pores 186 

Hydnaceae 359 

Hydnum repandum 361 

HydrocaryaceaB 427 

Hydrodictyon 318 

Hydrophytes, or water plants.... 452 

Hydropteridales 388 

Hydrotropism 285 

Hygroscopism, as an agent for 

the dispersion of fruits 113 

Hymenium of Fungi 353 

Hymenogastraceas 358 

Hymenomycetes 358 

Hypanthium 78 

Hypericaceaa 426 

Hyphae of fungi 340 

Hypocotyl 126 

Hypodermis 182 

Hypogeous germination 127 

INDETERMINATE Anthotaxy. . 61 

Inflorescence • 60 

Influence of light on the plant.. 279 

Influence of temperature on growth 278 

Insectivorous plants 53 

Insects and flowers 96 

Intercellular spaces 208,211 

Inulin 139 

Iridaceae 415 

Iris, floral diagram of 412 

Irregular flowers 75 

Irritability, in plants 255,288 

Isoetes, general characters of 395 

Isogametes 316 



JOINT Firs 407 

Juglandacesa 421 

Juglandales 421 

Tuncaceae 416 

Jungermanniales 375 

KARYOKINESIS 168 

Kernel 125 

LABIAT2E 430 

Lamarck, on evolution 433 

Lamina 37 

Laminaria 333 

Latex cells 205 

Laticiferous vessels 209 

LauracesB 423 

Laws, Mendelian 440 

Law of dominance 440 

Leaf, blade of 39 

centric 245 

dorsi-ventral 244 

epidermis of 241 

isolateral 245 

" fibro-vascular system of. . . . 241 

" histology of 241-246 

Leaf-scars 22 

Leaflets 50, 51 

Leaves, alternate 35, 36 

" apex forms 45 

" arrangement of 35 

" as insect-traps 53 

" base forms 46 

" cauline 37 

" compound 50 

" definition of 32,240 

" duration of 37 

floral 37 

foliage 32 

" functions of 32 

" general outline 44 

" marginal indentations ... 46 

" mode of growth of 32 

" modifications of 32 

" opposite 35 

" parts of 37 

" perfoliate 39 

" persistent 37 

" position of 37 

" radical 37 

" rameal 37 

" seminal 37 

" sessile 38 

" simple 44 

" structure of 37, 41, 240 

" surface of 51 

" texture of 52 

" venation of . 41 

" vernation of 33 

" whorlcd . . . 35 

Lecythidaceae 427 

Legume 119 

Leguminosae 424 

Lejolisia Mediterranea 338 

Lemnaceaa 415 

Lentibulariaceae 431 

Lenticels 238 

Leptome . . . 218 

Leptosporangiatae 382 

Leucoplasts 137 

Liber 239 

Libriform cells 197 

Lichen-alga? 363 

Lichenes 363 

Lichens, apothecium of 365 

" classification of 368 



462 



INDEX. 



crustaceous 366 

" foliaceous 366 

" fruticose 336 

" fructification of 365 

" heteromerous 365 

" homoiomerous 365 

" soredia of 365 

Lichen-fungi 363 

Light, in relation to plant life. 279, 446 

Ligule 40 

Liliaceas 415 

Liliales 415 

Limnanthacese 425 

Linaceae 425 

Litmus 367 

Liverworts 372 

Locomotion of plants 281 

Loganiaceae 429 

Loment 119 

Loranthaceaa 421 

Lycoperdacea? 358 

Lycopodiaceae 391 

Lycopodiales 391 

Lycopodinea?, general characters of 391 

Lycopodium 392 

Lysigenous passages 212 

Lythraceas 427 

MALVACEiE 426 

Malvales 426 

Manubrium 332 

Marantaceae 416 

Marasmus oreades 361 

Marchantiaceas 374 

Marchantia polymorphia 374 

Marsh plants 451 

Marsilia 387 

Martyniaceaa 431 

Medical botany 13 

Medulla 231 

Medullary rays 220, 231 

Megasporangia 106, 394 

Megaspore 106, 394 

Melastomaceaa 427 

Meliaceae 425 

Mendelism 439 

Mendel, researches of 440 

Meristematic tissue 176 

Meristems, primary 176 

primordial 176 

" secondary 176 

Mesocarp 118, 249 

Mesocarpus 327 

Mesophyll 41, 243 

Mestome 204, 205 

Mestome strand 231 

Mesophytes, or normal plants 452 

Metabolism 255 

Micrococcus 306 

Microsomes 134 

Microsporangia 106, 394 

Microspores 105, 382,394 

Midrib 242 

MimosaB 424 

Mineral substances in cells 153 

Mitosis 170 

Mobility of protoplasm 245 

Monoecious plants 97 

MonimiaceaB 423 

Monocotyledons, classification of. 413 

" embryo of 413 

flowers of . 412 

general charac- 
ters of . .411, 412 

" leaves of 412 



" orders of ...413-416 

" roots of 218, 412 

seeds of 412 

stems of 236, 412 

Monocotyledon-type of stem. . .226-231 

Monopodial branching 55 

Monotropaceaa 428 

Morphology 13 

Morchella esculenta 361 

Mosses 368, 369 

" antheridia of 369 

" archegonia of 369 

" calyptra of 371 

" classification of 372 

" columella of 371 

" elaters of 371 

" orders of 372-378 

" paraphyses of 369 

" perichastium of 369 

" perigynium of 369 

" protonema of 372 

spores of 372 

" sporogonium of 370 

" sporophyte of 370 

Movements of plants 280 

Movements, nyctitropic 286 

streaming 282 

Mucilage 143 

Mucilage-sacs 450 

Mucor Mucedo 341, 342 

Musaceae 416 

Musci 376 

Mutants 437 

Mutations as related to evolution.. 437 

Mutualism 275 

Mycelium of Fungi \ 340 

Mycorhiza 18, 276 

Myoporaceae 431 

Myricales 420 

Myricaceae 420 

Myrisinaceae 429 

Myristicaceae 423 

Myrtales 426 

Myrtaceae 427 

Myxomycetes 302 

NAMES, botanical, origin of 297 

Naming of plants 297 

Negative geotropism 283 

Negative heliotropism 283 

Nitrogen, fixation of 272 

Nolanaceae ,. 430 

Nomenclature, binomial 297 

Nostoc 309 

Nucleoli 135 

Nucleus 135 

Nut, or plans v 117 

Nyctitropic movements 286 

Nymphaceaa 423 

OBLIGATE Parasites 340 

Ocrea 41 

CEdogoniums 323, 324 

Offset 27 

Oil-cells 210 

Oils, fixed 143 

" volatile 150 

Oleaceaa 429 

Oleaceas, floral diagram of 418 

Oleo-resins 151 

Onagraceae 427 

Ontogeny 433 

Oospore 341 

Open collateral bundles 220 

Operculum of Mosses 370 



INDEX. 



463 



Ophioglossum 383 

Opuntiales 426 

Orchidales 416 

Orchidacea) 416 

Organography, defined 13 

Organs of plants, histology of. . . . 216 

Organs of reproduction 15, 58 

Organs of vegetation 15, 16 

Oscillatorias 310 

Osmosis 264 

Outer morphologv 14 

Ovary 88. 248 

Ovule, fertilization of 107 

Ovules, nature of 93 

" of Gymnosperms 399 

" position of 93 

" shapes of 94 

structure of 93 

Oxalidacea? 425 

PALEiE of Ferns 385 

Paleobotany 13 

Palisade tissue 178, 245 

Palms, useful products of 414 

Palmales 414 

Palmacea? 414 

Pandanales 413 

Pandanacese 413 

Pandorina 320 

Papaverales 423 

Papaveraceas 423 

Papilionacea? 424 

Papilla 182, 187 

Parallel venation 42,242 

Paraphyses .* 353 

Parasites 275 

" roots of 17 

Parenchyma 177 

folded 178 

palisade 178, 245 

pitted 178 

spongy 176, 245 

stellate 178 

Parenchymatous tissue 177 

Parietales 425 

Passifloracea? 426 

Pedaliacea* 431 

Pediastrum 318 

Pedicel 60 

Peduncle 60 

Penicillium glaucum 347, 348 

Pentosides 148 

Pepo 118 

Perennial herb 25 

Perennials 16 

Perianth 77, 80 

Periblem 216 

Pericarp 118, 249 

Perichaetium of Mosses 369 

Pericycle 224 

Periderm 238 

Peridinae 312 

Perigone 77 

Perigynium of Mosses 369 

Perisperm 109, 251 

Perisporiales 348 

Peronospora alsinearum 344 

Petals 79 

Petiole 37 

Petiolule 50 

Pezizales 351 

Phacidae 351 

Phaaophycese, or Brown Alga?.... 333 

Phaaosporales 333 

Pharmaceutical Botany 13 



Phascum muticum 371 

Phellogen 219, 238 

Phenotypes 444 

Phloem 205, 218 

Photogenic, bacteria 307 

Photosynthesis 255, 269 

Photosynthetic equation 269 

Phototropism 283 

Phrymacea? 431 

Phycomvcetes 341 

Phvllodia 39 

Phyllotaxy 35 

Phvlogenetic relationship 295 

Phvlogenv 433 

Physiology 13, 14. 254 

Phytophthora infestans 343, 344 

Pileus of Agarics 360 

Pinus sylvestris, reproduction in . . 404 

Piperales 420 

Pistils 71, 78 

" angiospermous 88 

apocarpous 89 

compound 89 

" gymnospermous 88 

placentation of 90 

" syncarpous 89 

Pitcher-plant 53 

Pith 231 

Pitted tracheids of pine 198, 200 

Pitted vessels 202 

Placentation 90 

Planococcus 307 

Planosarcina 307 

Plant breeding 13 

" classification 13 

hairs 186 

" industry 13 

" pathology 13 

" societies 451 

Plantaginales 43 1 

Planta & inaceae 431 

Plants, dioecious 74 

" monoecious 74 

" polygamous 74 

" principal groups of 299 

Plasmodia of Myxomycetes 302 

Plasmolysis 265 

Plectascales 348 

Plerome 217 

Pleurococcus 317 

Plocamium 337, 338 

Plumbaginacea? 429 

Plumule 127 

Polemoniales 430 

Polemoniacese 430 

Pollen, forms of 86, 250 

Pollen-tube 86. 106 

Pollinia 87 

Pollination 94 

Polvgalaceae 425 

Polypetalae 422 

Polypetalous corolla 80 

Polypodiaceaa 385 

Polyporacea? 359 

Polyporous fomentarius 359 

Polysepalous calyx 77 

Polytrichum commune 370 

Pome . 118 

Pontederiacea? 415 

Positive geotropism 283 

Positive heliotropism 283 

Prefloration 69 

Prefoliation 33 

Prickles 189 

Primary cortex 216 



464 



INDEX. 



" meristems 176, 216 

" structure of roots 218 

" permanent tissues 216 

Primulales 428 

PrimulaceJE 429 

Primitive Monocotyledons . 413 

Primitive Dicotyledons 420 

Principal groups of plants 299 

Procarps 337 

Pro-embryo . . 108, 406 

Prosenchymatous tissues 194 

Proterandrous flowers 97 

Proterogynous flowers 97 

Proteales 421 

Proteins 144 

Prothallium of Equisetine;v 389 

Ferns . . 381 

Lvcopodiacea> .... 391 

Mosses 380 

Pines 406 

Protococcales 317 

Protonema of Mosses $72, 376 

Protoplasm 135 

attributes of 254 

Trotoderm 216 

Protoplasts 132 

Protoxylem 232 

Pteridophyta, classes of 382 

" general characters of 379 

reproduction of ... 380 

Ptomains 308 

Pteris aquilena 224, 384 

Pteridosperms 399 

Puccinia graminis, life history of. 354 

Pulvinus 39 

Punicaceoe 427 

Purity of Gametes 441 

Putrefaction, cause of 308 

Pvrenolichenes 368 

Pyrenoid 320, 327 

Pyronema confluans 351 

Pyrolaceae 428 

Pyrenomycetes 348 

RACEME 62 

Rachis 60 

Radial bundles 218 

Radicle 126 

Rafflesia, flower of 97. 421 

Ranales 423 

Ranunculaceas 423 

Raphides 155 

Receptacle 76, 247 

Recessives and dominants 440 

Red Algse 336 

Reduction division 171 

Relation of Ecology to medicinal 

plants 454 

Relations of plants and animals... 450 

Reproduction, asexual 290 

sexual 290, 291 

spore 290, 291 

vegetative 290 

Resedacea? 424 

Resemblance between plants and 

animals 255. 276 

Resins 151 

Respiration 256. 276 

aerobic 277 

anaerobic 277 

Resting cells . . 310 

Reticulate venation 42, 243 

Reticulate vessels 203 

Rhamnales 426 

Rhamnacere ■ 426 



Rhizoids 222, 300 

Rhizomes distinction from roots. . 27 

Rhizophoraceae 427 

Rhodophyce.T 336 

Rhoeadales 423 

Ricciales 373 

Ricinus, germination of 419 

Rings of growth 236 

Rivularias 311 

Roccella tinctoria 367 

Root, definition of 16 

" histology of 216 

." how it differs from the stem 17 

Root-branches, origin of 221 

Root-cap 17, 217 

Root-hairs 18. 216. 263 

Root-pressure 266 

Roots, absorbing surface of 17 

" absorption by 265 

" forms of 19, 20 

functions of 16, 20 

" of Dicotyledons 218, 417 

" " Epiphytes 17 

" Monocotyledons ....218, 412 

" parasites 17 

" primary structure of...... 218 

" primary 18 

" secondary changes in 219 

tap 19 

" tuberous 19, 20 

Rosacese 424 

Rosales 424 

Rosette crystals 155 

Rubiaceas 431 

Rubiales 431 

Runner 27 

Rusts 354 

Rutaceas 425 

SACCHAROMYCES cefevisise.. . . 352 

Saccharomycetes 342 

Sage, flower of 102 

Salvinia natans 387 

Salicales 420 

Salicaceas 420 

Samara 116 

Sand soils 449 

Santalales 421 

Santalaceae 421 

Sapindacere 426 

Sapindales 425 

Sapotaceae 429 

Saprogenic bacteria 307 

Saprophytes 275 

Saprolegniales 343 

Sap-wood 235 

Sargassum 451 

Sarcina 306 

Sarcocarp 118, 249 

Sarraceniales 424 

Sarraceniaceae 424 

Saxifra aceaa . 424 

Scalariform vessels 202 

Scape 26, 60 

Scenedesmus 317 

Schizogenous passages 212 

Schizomycetes 305 

Scitaminales 416 

Sclerenchyma fibers 194 

Sclerotia of Myxomycetes 303 

Sclerotic tissue 180 

Sclerotium of Fungi 340. 348 

Scrophulariaceas 430 

Scytonemas 310 

Seacoast plants, or Halophytes . . . 453 



INDEX 



465 



Secondary medullary rays 232 

" meristems 176 

permanent tissues .... 176 

" structure of roots 219 

xylem 219 

Secretion cells 210 

" passages 212 

" tissues 206 

Seed, coats of 123, 249 

" definition of 123 

" number of 129 

" internal structure of.... 125, 249 

Seeds, dispersion of 113 

Selaginella 394 

Selaginellales, general characters of 393 

Semi-parasites 275 

Sepals 71, 247 

Sieve plates 204 

Sieve tissue 204 

Simarubacese j 425 

Siphonales 315 

Sleep movements 286 

Slime-molds 302 

Smut-fungi 357 

Soil as an ecological factor 448 

Soils, various kinds of 449 

Solanaceae 430 

Soredia of Lichens 365 

Sorus of Ferns 382 

Spadix \ 63 

Sparganiaceae 413 

Specialized Monocotyledons 416 

Specialized Dicotyledons 428 

Spermagonia of Ascomycetes 355 

Spermatophyta, classification of. . . 398 
Spermatophyta, general characters 

of , 396 

Spermatia of Ascomycetes 355 

Spermoderm 124, 249 

Sperms, or male gametes 105 

Sphagnales 376 

Sphagnum 377 

Spike 62 

Spines 27 

Spiral vessels 202 

Spirillum 306, 307 

Spirochasta 307 

Spirogyra 327 

Sporangia of Ferns 380 

Spore-reproduction 290, 291 

Sporidia 344, 345 

Sporogonium of Mosses 370 

Sporophyte of Mosses 370 

Sports, or Mutants 437 

Starch as reserve food-material . 138, 271 

formation of 138, 139 

" in chloroplasts 138 

" storage of 138 

Starch-grains, forms of 139 

" " structure of 138 

Stamens 71, 82, 247 

" parts of 82 

Staminodia 84 

Staphylaceas 425 

Staphylococcus 306 

Starch sheath 218 

Stele 217 

Stems, definition of 20 

" direction of growth of. . . . 25 

" duration of 25 

" habits of growth of 25 

" how they differ from roots 20 

leaf-like 30 

" size of 24 

" shapes of 24 



" underground 27 

Sterculiacea; 426 

Stereome 180 

Sticta pulmonacea 367 

Stigma, structure of 92, 248 

Stipules, modification of 37 

Stolon 26 

Stomata 182 

" number to the square inch 184 

Stone cells 180 

Storage of reserve materials 273 

Stramonium, fruit of 113 

Streaming movements 282 

Streptococcus 306 

Strobile 63 

Strobilus of Fquisetums 388 

Struggle for existence 435 

Style 92 

Styraceae 429 

Suberin 163 

Suberous tissue 191 

Substratum 340 

Succession of Plant Societies.... 454 

Sucker 27 

Sugars 140 

Survival of the fittest 435 

Sundew 53 

Suspensor 108, 194 

Suture 89 

Swamp societies of plants 452 

Symbionts 275 

Symbiosis 275 

Sympetala3 427 

Symplocaceoa 429 

Syncarpous pistils 89 

Synergidfe 107, 410 

Synthesis of carbohydrates 269 

Synthesis of proteins 271 

Systematic botany 13 

TAMARICACE^E 426 

Taxus baccata, flowers of 403 

Taxonomy, vegetable 13, 14, 294 

Teleutospores 354, 355 

Temperature in relation to plant life 278 

Tendrils, nature of 26 

Testa 124, 129 

Tetraspores 337 

Thallophyta, general characters of 300 

Thallus 30 

Theaceaa 426 

Thelephoracese 359 

Thermogenic bacteria 307 

Thermotropism 285 

Thorns 27 

Thymeleaceae 426 

Thyrsus 68 

Tiliaceae 426 

Tissues, classification of 175 

" origin of 175 

Torus 76 

Toxins 308 

Trabecular vessels 203 

Tracheal tubes 201 

Tracheids 198 

of Gymnosperms ...198, 199 

Transpiration 267 

Transverse geotropism 283 

Trichogyne of Red Algaa 338 

Trichomes 186 

Tropaeolaceae 425 

Truffles 352 

Tryma 118 

Tuberaceas _ 352 

Tubers, characteristics of 28 



466 



INDEX. 



Turgor 265 

Tyloses ' 204 

Typhacese 413 

ULVA LACTUCA 323 

Umbilicaria vellea 367 

Umbel 62 

Umbellales 427 

Umbelliferse 427 

Underground stems 27 

" uses of 29 

Unit characters, or genes 441 

Unorganized ferments 146 

Uredinales 354 

Uredospores 340, 354 

Uroglena 312 

Urticaceae 421 

Urticales 421 

Usnea barbata 367 

Ustilago maidis 357 

Ustilaginales 357 

Utricle 116 

VACUOLES 134 

Valvate prefloration 69 

Valerianaceae 431 

Vascular bundles, collateral, open. 220 
" collateral, closed 226 

" concentric 224 

radial 218 

" cryptogams 379 

" tissues 201 

Vaucherias 316 

Vegetative organs 15, 16 

Velum of A arics 360 

Venation, forked 41 

of leaves 41, 242 

parallel 42, 242 

reticulate 42, 243 

Verbenaceas 430 



Vernation 33 

Verticillales 420 

Verticillaster 67 

Vessels 201, 202 

Violaceas 426 

Vitacese 426 

Volatile Oils 150 

Volvocales 319 

Volvox globator 321 

WATER, as an ecological factor. . 448 

Water plants, or hydrophytes.... 451 

Water in plants 259 

Water-pores 186 

Waxes 143 

Weeds 450 

Welwitschia 407 

Wilting of leaves 267 

Wind, as an ecological factor.... 450 

Wood fibers 197 

Wood parenchyma 201 

Wound cork 193 

XEROPHYTES, or desert plants 453 

Xylem 197 

" primary 219 

" secondary 219 

YEAST Fungi 352 

Yeast-plant 352 

ZINGIBERACE2E 416 

Zooglfea-masses of Bacteria 305 

Zoospores 316 

Zygnema 327 

Zygomycetales 341 

Zygophyllaceas 425 

Zygospores .316, 341 

Zymogenic bacteria 307 



